firmware: arm_ffa: Add support for FFA_PARTITION_INFO_GET_REGS

firmware: arm_ffa: Add support for FFA_PARTITION_INFO_GET_REGS

FF-A v1.2 introduced FFA_PARTITION_INFO_GET_REGS which is similar to
FFA_PARTITION_INFO_GET except that the former uses the registers to
get the required information instead of the Rx buffer which the latter
uses.

We need to first check if the platform supports this new API using
FFA_FEATURES so that we can fallback to the FFA_PARTITION_INFO_GET
(which is mandatory) if FFA_PARTITION_INFO_GET_REGS is not implemented.

Message-Id: <20240820-ffa_v1-2-v2-4-18c0c5f3c65e@arm.com>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>