drm/radeon/kms: only change mode when coherent value changes.
drm/radeon/kms: only change mode when coherent value changes.

On X startup we were getting a flicker where there shouldn't have been one.
the X DDX calls the kernel to set the properties to the same values (yes
it could be smarter), however the kernel was doing a pointless modeset then,
making my nice smooth boot ugly.

Signed-off-by: Dave Airlie <f2295d84e358395675bc8031be58672073ae065e@redhat.com>

KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,KristFoundation/Programs