drm/i915/skl: Swapping 90 and 270 to be compliant with Xrandr

Since DRM_ROTATE is counter clockwise (which is compliant with Xrandr),
and HW rotation is clockwise, swapping 90/270 to work as expected from
userspace.

v2: Rebased

Suggested-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Sonika Jindal <sonika.jindal@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>