Staging: sxg: Add support to download the firmware using request_firmware()

Add support for downloading the firmware using kernel-builtin mechanism.
This will remove the need for the firmware files in the driver source code.

Signed-off-by: Christopher Harrer <charrer@alacritech.com>
Signed-off-by: Mithlesh Thukral <mithlesh@linsyssoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>