android/bootloaders*: upreve optee_{os,_client,test} to upstream 4.2.0 tag

This is the same version as used in meta-ti yocto layer:

https://git.ti.com/cgit/arago-project/meta-ti/tree/meta-ti-bsp/recipes-security/optee/optee-os-ti-version.inc



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