firmware: ti_sci: Allow for device shared and exclusive requests

Sysfw provides an option for requesting exclusive access for a
device using the flags MSG_FLAG_DEVICE_EXCLUSIVE. If this flag is
not used, the device is meant to be shared across hosts. Once a device
is requested from a host with this flag set, any request to this
device from a different host will be nacked by sysfw. Current tisci
driver enables this flag for every device requests. But this may not
be true for all the devices. So provide a separate commands in driver
for exclusive and shared device requests.

Signed-off-by: Lokesh Vutla <lokeshvutla@ti.com>