drm/i915: Introduce intel_crtc_{alloc,free}()

We already have alloc/free helpers for planes, add the same for
crtcs. The main benefit is we get to move all the annoying state
initialization out of the main crtc_init() flow.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191107142417.11107-3-ville.syrjala@linux.intel.com


Reviewed-by: José Roberto de Souza <jose.souza@intel.com>