drm/radeon/kms: fix DP training for DPEncoderService revision bigger than 1.1

DPEncoderService newer than 1.1 can't properly program the DP (display port)
link training. When facing such version use the DIGxEncoderControl method
instead. Fix DP link training on some R7XX.

Signed-off-by: Jerome Glisse <jglisse@redhat.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@kernel.org
Signed-off-by: Dave Airlie <airlied@redhat.com>