drm/i915: create intel_update_pipe_size()

drm/i915: create intel_update_pipe_size()

Factor out a piece of code from intel_pipe_set_base() that updates
the pipe size and adjust fitter.

This will help refactor the update primary plane path.

v2: use struct intel_crtc as argument to intel_update_pipe_size()

v3: use 'crtc' as argument name

Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>