bootstd: android: don't read whole partition sizes

bootstd: android: don't read whole partition sizes

The current implementation is reading the whole partition for boot and
vendor_boot image which can be long following the size of the
partition or the time to read blocks (driver/SoC specific).

For example with mediatek mt8365 EVK board, we have a 64MiB boot
partition and the boot image flashed in this partition is only 42MiB.
It takes ~8-9 secs to read the boot partition.

Instead we can retrieved the boot image and vendor boot image size
with these new functions:
- android_image_get_bootimg_size
- android_image_get_vendor_bootimg_size
Use these information and read only the necessary.

By doing this with mt8365 EVK board, we read boot image in ~5 secs.

Signed-off-by: Julien Masson <jmasson@baylibre.com>
Reviewed-by: Mattijs Korpershoek <mkorpershoek@baylibre.com>
Link: https://lore.kernel.org/r/20241121-bootmeth-android-part-sizes-v1-1-25760bbd0f08@baylibre.com
Signed-off-by: Mattijs Korpershoek <mkorpershoek@baylibre.com>