drm/tidss: dispc: Get rid of FLD_MOD

The FLD_MOD function is an equivalent to what FIELD_MODIFY + GENMASK
provide, so let's drop it and switch to the latter.

Signed-off-by: Maxime Ripard <mripard@kernel.org>
Link: https://lore.kernel.org/r/20250827-drm-tidss-field-api-v3-6-7689b664cc63@kernel.org


Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>