drm/i915: Fix 90/270 degree rotated RGB565 src coord checks

Supposedly both src coordinates have to even when doing 90/270
degree rotation with RGB565. This is definitely true for the
X coordinate (we just get a black screen when it is odd). My
experiments didn't show any misbehaviour with an odd
Y coordinate, but let's trust the spec and reject that one
as well.

v2: Ignore ccs hsub/vsub
v3: Clarify the CCS special (Maarten)
    Deal with tgl+ CCS modifiers where we
    do need to look at hsub/vsub

Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com> #v2
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200228160523.1064-1-ville.syrjala@linux.intel.com