This is a translation of the patch ...
"drm/radeon: Handle irqs only based on irq ring, not irq status regs."
... for the vblank irq handling, to fix the same problem described
in that patch on the new driver.

Only compile tested due to lack of suitable hw.
Reviewed-by: NChristian König <christian.koenig@amd.com>
Signed-off-by: NMario Kleiner <mario.kleiner.de@gmail.com>
CC: Michel Dänzer <michel.daenzer@amd.com>
CC: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>