arm64/sysreg: Standardise naming for ID_ISAR0_EL1

arm64/sysreg: Standardise naming for ID_ISAR0_EL1

To convert the 32bit id registers to use the sysreg generation, they
must first have a regular pattern, to match the symbols the script
generates.

Ensure symbols for the ID_ISAR0_EL1 register have an _EL1 suffix,
and use lower-case for feature names where the arm-arm does the same.

To functional change.

Signed-off-by: James Morse <james.morse@arm.com>
Link: https://lore.kernel.org/r/20221130171637.718182-5-james.morse@arm.com
Signed-off-by: Will Deacon <will@kernel.org>