drm/i915: Extract per-platform plane->check() functions

Split up intel_check_primary_plane() and intel_check_sprite_plane()
into per-platform variants. This way we can get a unified behaviour
between the SKL universal planes, and we stop checking for non-SKL
specific scaling limits for the "sprite" planes. And we now get
a natural place where to add more plarform specific checks.

v2: Split the .check_plane() calling convention change out (José)

Reviewed-by: José Roberto de Souza <jose.souza@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180907152413.15761-10-ville.syrjala@linux.intel.com