drm/radeon: Restore sw interrupt on resume

Fixes performance drop after suspend/resume on some systems.

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

diff --cc drivers/char/drm/radeon_cp.c
Simple merge

diff --cc drivers/char/drm/radeon_drv.h
Simple merge

diff --cc drivers/char/drm/radeon_irq.c
Simple merge