docs: add a section for experimental build options
A number of features are marked experimental in the build system through
makefiles but there wasn't an explicit document to list them.
Added a dedicated experimental build options section and moved
existing experimental build option descriptions in this section.
Restoring the change from [1] removing the experimental flag on the EL3
SPMC (this has been lost in rebasing a later change).
[1] https://review.trustedfirmware.org/c/TF-A/trusted-firmware-a/+/24713
Signed-off-by: Olivier Deprez <olivier.deprez@arm.com>
Change-Id: I2c458c6857c347114b265404e8b9ede9ac588463
2 files changed