fix(cpufeat): move nested virtualization support to optionals

Commit(f5211420b refactor(cpufeat): refactor arch feature build
options) accidentally added nested virtualization support to mandatory
8.4 features move this to optional 8.4 features list.

Signed-off-by: Govindraj Raja <govindraj.raja@arm.com>
Change-Id: I3eb84ea489b6a5cc419359bc056aaadcced0ad0e
1 file changed