firmware: ti_sci: Add helper apis to manage resources

Each resource with in the device can be uniquely identified as defined
by TISCI. Since this is generic across the devices, resource allocation
also can be made generic instead of each client driver handling the
resource. So add helper apis to manage the resource.

Signed-off-by: Lokesh Vutla <lokeshvutla@ti.com>
Acked-by: Nishanth Menon <nm@ti.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>