firmware: ti_sci: Provide host-id as an optional dt parameter

Texas Instrument's System Control Interface (TISCI) permits the
ability for Operating Systems to running in virtual machines to be
able to independently communicate with the firmware without the need
going through an hypervisor.

The "host-id" in effect is the hardware representation of the
host (example: VMs locked to a core) as identified to the System
Controller.

Provide support as an optional parameter implementation and use the
compatible data as default if one is not provided by device tree.

Signed-off-by: Nishanth Menon <nm@ti.com>
Signed-off-by: Santosh Shilimkar <santosh.shilimkar@oracle.com>