arm64: Take into account ID_AA64PFR0_EL1.CSV3

arm64: Take into account ID_AA64PFR0_EL1.CSV3

commit 179a56f6f9fb upstream.

For non-KASLR kernels where the KPTI behaviour has not been overridden
on the command line we can use ID_AA64PFR0_EL1.CSV3 to determine whether
or not we should unmap the kernel whilst running at EL0.

Reviewed-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Alex Shi <alex.shi@linaro.org>
Conflicts:
	skip cpu features like SVE etc.
	and use 5 paramaters function ARM64_FTR_BITS()
	replace read_sanitised_ftr_reg with old name read_system_reg
	arch/arm64/include/asm/sysreg.h
	arch/arm64/kernel/cpufeature.c