The SI UVD firmware validate key is stored at the end of firmware,
which is changed during resume while playing video. So get the key
at sw_init and store it for fw validate using.

Signed-off-by: Sonny Jiang <sonny.jiang@amd.com>
Reviewed-by: Leo Liu <leo.liu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org