firmware: arm_scmi: Simplify chan_available transport operation

firmware: arm_scmi: Simplify chan_available transport operation

SCMI transport operation .chan_available determines in a transport
specific way if an SCMI channel is still available and to be configured.
Such information is derived by analyzing bits of device node in a
transport specific way, all it needs is a device node to operate up on,
not necessarily a full blown device.

Simplify the helper to receive in input a reference to a device_node
instead of a device carrying a pointer to such device_node.

Signed-off-by: Cristian Marussi <cristian.marussi@arm.com>
Link: https://lore.kernel.org/r/20221222185049.737625-2-cristian.marussi@arm.com
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>