drm/i915: Sipmplify PLANE_STRIDE masking

drm/i915: Sipmplify PLANE_STRIDE masking

There's no need to have separate masks for the stride bitfield
in PLANE_STRIDE for different platforms. All the extra bits
are hardcoded to zero anyway.

Also the masks we're using now don't even match the actual hardware
since the bitfield was only 10 bits on skl/derivatives, only getting
bumped to 11 bits on glk.

So let's just use a 12 bit mask for everything.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20211201152552.7821-5-ville.syrjala@linux.intel.com
Reviewed-by: José Roberto de Souza <jose.souza@intel.com>