drm/i915: Fix wrongly populated plane possible_crtcs bit mask

As a disabled pipe in pipe_mask is not having a valid intel crtc,
driver wrongly populates the possible_crtcs mask while initializing
the plane for a CRTC. Fixing up the plane possible_crtcs mask.

changes since RFC:
- Simplify the possible_crtcs initialization. [Ville]
v2:
- Removed the unnecessary stack garbage possible_crtcs to
  drm_universal_plane_init. [Ville]
v3:
- Combine the intel_crtc assignment and declaration. [Ville]
v4:
- Fix possible_crtcs abused bits from
  intel_{primary,curosr,sprite}_plane_create(). [Ville]

Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Anshuman Gupta <anshuman.gupta@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200226163517.31234-1-anshuman.gupta@intel.com