bootloaders: Use ti-u-boot-2024.04 by default

We temporarily had 2 set of support bootloaders:
- 2023.04
- 2024.04

Now that the SDK 10.0 release is out, remove the 2023.04 U-Boot
and use 2024.04 by default.

Signed-off-by: Mattijs Korpershoek <mkorpershoek@baylibre.com>