fix(debugv8p9): fix access to mdselr_el1

When 16 or fewer breakpoints are implemented, MDSELR_EL1 is
implemented as RAZ/WI, it is IMPLEMENTATION DEFINED whether
the trap controls have any effect on accesses to MDSELR_EL1.

Ref: https://developer.arm.com/documentation/111107/2025-09/AArch64-Registers/MDSELR-EL1--Breakpoint-and-Watchpoint-Selection-Register?lang=en

Change-Id: I40215ca074e01d5e5dfb184c6aba656fc9077018
Signed-off-by: Govindraj Raja <govindraj.raja@arm.com>
5 files changed