arm64: add HWCAP for FEAT_HBC (hinted conditional branches)

Add a HWCAP for FEAT_HBC, so that userspace can make a decision on using
this feature.

Signed-off-by: Joey Gouly <joey.gouly@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
Link: https://lore.kernel.org/r/20230804143746.3900803-2-joey.gouly@arm.com


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