firmware: arm_ffa: Add support for querying FF-A features

firmware: arm_ffa: Add support for querying FF-A features

Add support for FFA_FEATURES to discover properties supported at the
FF-A interface. This interface can be used to query:
 - If an FF-A interface is implemented by the component at the higher EL,
 - If an implemented FF-A interface also implements any optional features
   described in its interface definition, and
 - Any implementation details exported by an implemented FF-A interface
   as described in its interface definition.

Link: https://lore.kernel.org/r/20220907145240.1683088-5-sudeep.holla@arm.com
Reviewed-by: Jens Wiklander <jens.wiklander@linaro.org>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>