drm/tidss: dispc: Switch VP_REG_GET to using a mask

drm/tidss: dispc: Switch VP_REG_GET to using a mask

The VP_REG_GET function takes the start and end bits as parameter and
will generate a mask out of them.

This makes it difficult to share the masks between callers, since we now
need two arguments and to keep them consistent.

Let's change VP_REG_GET to take the mask as an argument instead, and let
the caller create the mask. Eventually, this mask will be moved to a
define.

Signed-off-by: Maxime Ripard <mripard@kernel.org>
Link: https://lore.kernel.org/r/20250827-drm-tidss-field-api-v3-11-7689b664cc63@kernel.org
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>