arm64/sysreg: Standardise naming for MVFR2_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 MVFR2_EL1 register use lower-case for feature
names where the arm-arm does the same.

No functional change.

Signed-off-by: James Morse <james.morse@arm.com>
Link: https://lore.kernel.org/r/20221130171637.718182-16-james.morse@arm.com


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