arm64/sysreg: Standardise naming for ID_AA64PFR0_EL1 constants

arm64/sysreg: Standardise naming for ID_AA64PFR0_EL1 constants

We generally refer to the baseline feature implemented as _IMP so in
preparation for automatic generation of register defines update those for
ID_AA64PFR0_EL1 to reflect this.

In the case of ASIMD we don't actually use the define so just remove it.

No functional changes.

Signed-off-by: Mark Brown <broonie@kernel.org>
Reviewed-by: Kristina Martsenko <kristina.martsenko@arm.com>
Link: https://lore.kernel.org/r/20220905225425.1871461-14-broonie@kernel.org
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>