arm64/sysreg: Make BHB clear feature defines match the architecture

The architecture refers to the field identifying support for BHB clear as
BC but the kernel has called it CLEARBHB. In preparation for generation of
defines for ID_AA64ISAR2_EL1 rename to use the architecture's naming. No
functional changes.

Signed-off-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20220704170302.2609529-11-broonie@kernel.org


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