refactor(cpufeat): convert FEAT_HCX to new scheme

Use the generic check function in feat_detect.c, and split the feature
check into two functions, as done for FEAT_FGT before.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Change-Id: I0a4f973427c10d5d15c414ff5e12b18b7e645fae
3 files changed