arm64/sysreg: Convert GMID to automatic generation

Automatically generate the register definitions for GMID as per DDI0487H.a,
no functional change.

Signed-off-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20220704170302.2609529-20-broonie@kernel.org


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