arm64/sysreg: add system register POR_EL{0,1}

Add POR_EL{0,1} according to DDI0601 2023-03.

Signed-off-by: Joey Gouly <joey.gouly@arm.com>
Reviewed-by: Mark Brown <broonie@kernel.org>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20231209-b4-arm64-sysreg-additions-v1-3-45284e538474@kernel.org


Signed-off-by: Will Deacon <will@kernel.org>