drm/i915: Add a wrapper function around get_pipe_config

Create a new function intel_crtc_get_pipe_config()
that calls platform specific hooks for get_pipe_config()
No functional change here.

Suggested-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Manasi Navare <manasi.d.navare@intel.com>
[vsyrjala: Conform to modern i915 coding style, fix patch subject]
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Manasi Navare <manasi.d.navare@intel.com>
Reviewed-by: Animesh Manna <animesh.manna@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20201112191718.16683-3-ville.syrjala@linux.intel.com