bootstd: Add Android support

Android boot flow is a bit different than a regular Linux distro.
Android relies on multiple partitions in order to boot.

A typical boot flow would be:
1. Parse the Bootloader Control Block (BCB, misc partition)
2. If BCB requested bootonce-bootloader, start fastboot and wait.
3. If BCB requested recovery or normal android, run the following:
   a. Get slot (A/B) from BCB
   b. Run AVB (Android Verified Boot) on boot partitions
   c. Load boot and vendor_boot partitions
   d. Load device-tree, ramdisk and boot

The AOSP documentation has more details at [1], [2], [3]

This has been implemented via complex boot scripts such as [4].
However, these boot script are neither very maintainable nor generic.
Moreover, DISTRO_DEFAULTS is being deprecated [5].

Add a generic Android bootflow implementation for bootstd.

For this initial version, only boot image v4 is supported.

This has been tested on sandbox using:
$ ./test/py/test.py --bd sandbox --build -k test_ut

This has also been tested on the AM62X SK EVM using TI's Android SDK[6]
To test on TI board, the following (WIP) patch is needed as well:
84cceb91

[1] https://source.android.com/docs/core/architecture/bootloader
[2] https://source.android.com/docs/core/architecture/partitions
[3] https://source.android.com/docs/core/architecture/partitions/generic-boot
[4] https://source.denx.de/u-boot/u-boot/-/blob/master/include/configs/meson64_android.h
[5] https://lore.kernel.org/r/all/20230914165615.1058529-17-sjg@chromium.org/
[6] https://software-dl.ti.com/processor-sdk-android/esd/AM62X/09_02_00/docs/android/Overview.html



To: Simon Glass <sjg@chromium.org>
Cc: Julien Masson <jmasson@baylibre.com>
Cc: Guillaume La Roque <glaroque@baylibre.com>
Cc: Dmitrii Merkurev <dimorinny@google.com>
Cc: Roman Stratiienko <r.stratiienko@gmail.com>
Cc: Igor Opaniuk <igor.opaniuk@gmail.com>
Cc: u-boot@lists.denx.de
Signed-off-by: Mattijs Korpershoek <mkorpershoek@baylibre.com>

---
Changes in v3:
- Fixed CI issues (Tom):
  * Generate bootv4.img and vendor_boot.img in test_ut.py
  * Mark CONFIG_BOOTMETH_ANDROID dependent on CONFIG_CMDLINE
  * Make bootflow_android() test dependent on CONFIG_BOOTMETH_ANDROID
  Because of the above changes, I've removed the reviewers on patch 5/5
- Link to v2: https://lore.kernel.org/r/20240613-bootmeth-android-v2-0-397f6e66eb29@baylibre.com

Changes in v2:
- Dropped patch 2/6 boot: android: Add image_android_get_version() (Igor)
- Fixed multi-line comment style (Igor, Simon)
- Added dependency on CMD_FASTBOOT for BOOTMETH_ANDROID (Igor)
- Fixed various resource leaks (Igor)
- Fixed bootmeth_priv dangling pointer on error cases (Igor)
- Updated test instructions in commit message for patch 6/6
- Added __weak impl of get_avendor_bootimg_addr() in patch 1 (dropped
  Igor's review because of this change)
- Added extra info in Kconfig to detail MMC limitation (Simon)
- Fixed typo Bootmethod->Bootmeth (Simon)
- Documented android_priv structure (Simon)
- Demoted various messages from printf() to log_debug (Simon)
- Fixed some lines too long (Simon)
- Added function documentation to read_slotted_partition() (Simon)
- Added some doc about avb extra_args being modified (Simon)
- Link to v1: https://lore.kernel.org/r/20240606-bootmeth-android-v1-0-0c69d4457cc5@baylibre.com

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