drm: Remove fb hsub/vsub alignment requirement

drm: Remove fb hsub/vsub alignment requirement

Allow framebuffers dimesions to be misaligned w.r.t. the subsampling
factors. No real reason the core should have to enforce this, and
it definitely starts to cause us issues with the i915 CCS support.
So let's just lift the restriction.

Let's start to round up when computing the color plane dimesions
so that we'll not end up with too low an estimate for the memory
requirements and whatnot.

Cc: Ben Widawsky <ben@bwidawsk.net>
Cc: Jason Ekstrand <jason@jlekstrand.net>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170321181218.10042-3-ville.syrjala@linux.intel.com
Reviewed-by: Ben Widawsky <ben@bwidawsk.net>