soc: ti: use request_firmware_direct() as acc firmware is optional

When firmware image for PDSP firmware is absent in the file system
the kernel boot with ramfs/nfs is stuck for 60 seconds being the
the default timeout. request_firmware_direct() is to take care of
such optional firmware loading and hence replace the call in the
driver with this API.

Signed-off-by: Murali Karicheri <m-karicheri2@ti.com>
Signed-off-by: Santosh Shilimkar <ssantosh@kernel.org>