firmware: arm_scmi: Suppress the driver's bind attributes

Suppress the capability to unbind the core SCMI driver since all the
SCMI stack protocol drivers depend on it.

Fixes: aa4f886f ("firmware: arm_scmi: add basic driver infrastructure for SCMI")
Signed-off-by: Cristian Marussi <cristian.marussi@arm.com>
Link: https://lore.kernel.org/r/20221028140833.280091-2-cristian.marussi@arm.com


Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>