drm/msm/dpu: Remove dpu_crtc_is_enabled()

The static inline function dpu_crtc_enabled() is only called once
and the function that calls it in turn is only called once and
the return value can be easily checked in the calling functions
so collapse everything down.

v3: No changes

Reviewed-by: Sean Paul <sean@poorly.run>
Signed-off-by: Jordan Crouse <jcrouse@codeaurora.org>
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Signed-off-by: Rob Clark <robdclark@gmail.com>