KVM: arm64: Fold DBGxVR/DBGxCR accessors into common set

There is a nauseating amount of boilerplate for accessing the
breakpoint and watchpoint registers. Fold everything together into a
single set of accessors and select the right storage based on the sysreg
encoding.

Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
Link: https://lore.kernel.org/r/20241219224116.3941496-19-oliver.upton@linux.dev


Signed-off-by: Marc Zyngier <maz@kernel.org>