cmd: avb: rework do_avb_verify_part

Use existing str_avb_slot_error() function for obtaining
verification fail reason details.
Take into account device lock state for setting correct
androidboot.verifiedbootstate kernel cmdline parameter.

Reviewed-by: Mattijs Korpershoek <mkorpershoek@baylibre.com>
Signed-off-by: Igor Opaniuk <igor.opaniuk@gmail.com>
Link: https://lore.kernel.org/r/20240209192045.3961832-7-igor.opaniuk@foundries.io


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