firmware: arm_scmi: Add initial support for i.MX BBM protocol

i.MX95 has a battery-backed module(BBM), which has persistent storage
(GPR), an RTC, and the ON/OFF button. The System Manager(SM) firmware
use SCMI vendor protocol(SCMI BBM) to let agent be able to use GPR, RTC
and ON/OFF button.

Reviewed-by: Cristian Marussi <cristian.marussi@arm.com>
Signed-off-by: Peng Fan <peng.fan@nxp.com>
Message-Id: <20240823-imx95-bbm-misc-v2-v8-2-e600ed9e9271@nxp.com>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>