KVM: arm64: Define helper for EL2 registers with custom visibility

KVM: arm64: Define helper for EL2 registers with custom visibility

In preparation for adding more visibility filtering for EL2 registers add
a helper macro like EL2_REG() which allows specification of a custom
visibility operation.

Signed-off-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20240822-kvm-arm64-hide-pie-regs-v2-1-376624fa829c@kernel.org
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20241023145345.1613824-24-maz@kernel.org
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>