firmware: ti_sci: Add a command for releasing all exclusive devices

Any host while requesting for a device can request for its exclusive
access. If an exclusive permission is obtained then it is the host's
responsibility to release the device before the software entity on
the host completes its execution. Else any other host's request for
the device will be nacked. So add a command that releases all the
exclusive devices that is acquired by the current host. This should
be used with utmost care and can be called only at the end of the
execution.

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