refactor(build): allow mandatory feats disabling

Currently any arch FEAT_* can be enabled from:
 - command line build options
 - platform makefile
 - from arch_features.mk

These are in order. However, mandatory features are enforced from
arch_features.mk and platform makefile can't override them.

Allow command line options or platforms makefile to disable any
mandatory features.

Change-Id: I6fdca1a3d0b405a88cd7a20309e0c1eecd57a650
Signed-off-by: Govindraj Raja <govindraj.raja@arm.com>
1 file changed