Arch: Abstract the operation of prioritizing Secure exceptions

Add tfm_arch_prioritize_secure_exception() to abstract architecture
specific Secure exceptions priority boosting.
Implement tfm_arch_prioritize_secure_exception() on Armv8-M.

Change-Id: I61b8d75d23025032ced5bd4f2355981340df75f6
Signed-off-by: David Hu <david.hu@arm.com>
4 files changed