docs(build): update the feature enablement flags

Adding the newly introduced build flags for feature enablement of the
following features:
1.FEAT_AMUv1p1 - ENABLE_FEAT_AMUv1p1
2.FEAT_CSV2_2  - ENABLE_FEAT_CSV2_2
3.FEAT_VHE     - ENABLE_FEAT_VHE
4.FEAT_DIT     - ENABLE_FEAT_DIT
5.FEAT_SB      - ENABLE_FEAT_SB
6.FEAT_SEL2    - ENABLE_FEAT_SEL2

Also as part of feature detection mechanism, we now support three
states for each of these features, allowing the flags to take either
(0 , 1 , 2) values. Henceforth the existing feature build options are
converted from boolean to numeric type and is updated accordingly
in this patch.

The build flags take a default value and will be internally enabled
when they become mandatory from a particular architecture version
and upwards. Platforms have the flexibility to overide this
internal enablement via this feature specific explicit build flags.

Signed-off-by: Jayanth Dodderi Chidanand <jayanthdodderi.chidanand@arm.com>
Change-Id: I0090c8c780c2e7d1a50ed9676983fe1df7a35e50
1 file changed