drm/radeon: properly byte swap vce firmware setup

Firmware is LE.  Need to properly byteswap some of the fields
so they are interpreted correctly by the driver on BE systems.

Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org