drm/i915: Fix glk watermark calculations

GLK wants the +1 adjustement for the "blocks per line" value
for x-tile/y-tile, just like cnl+.

Also the x-tile and linear cases are almost identical. The only
difference is this +1 which is always done for glk+, and only
done for linear on skl/bxt. Let's unify it to a single branch
with a special case for the +1, just like we do for y-tile.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200430125822.21985-1-ville.syrjala@linux.intel.com


Reviewed-by: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>