drm/radeon: add radeon_fence_count_emited function

Split counting of emited fences out of power
management into a seperate function.

Signed-off-by: Christian König <deathsimple@vodafone.de>
Reviewed-by: Jerome Glisse <jglisse@redhat.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>