KVM: arm64: Get rid of ARM64_FEATURE_MASK()

The ARM64_FEATURE_MASK() macro was a hack introduce whilst the
automatic generation of sysreg encoding was introduced, and was
too unreliable to be entirely trusted.

We are in a better place now, and we could really do without this
macro. Get rid of it altogether.

Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20250817202158.395078-7-maz@kernel.org


Signed-off-by: Oliver Upton <oliver.upton@linux.dev>