arch-arm: Deprecate usage of legacy bootloader patching

arch-arm: Deprecate usage of legacy bootloader patching

This patch is implicitly deprecating the usage of bootloader patching,
which is injecting instructions from gem5 into the bootloader
binary. This was probably meant to provide a dynamic bootloader
entry point.
This is not needed in ARMv8.0, since we can simply update the
ArmSystem::resetAddress with the bootloader entry point.

Change-Id: I0c469873b8d69f7b49a7383e0754468bc1f2bd72
Signed-off-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/14001
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>