OMAPDSS: Features: Maintain dss_feats as a list

The number of dss_feat_id members has increased to a large value, the current
way of assigning a subset of these features (for a particular OMAP) as a mask
is no longer feasible.

Maintain the subset of features supported as lists. Make the function
dss_has_feature() traverse through this list.

Signed-off-by: Archit Taneja <archit@ti.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>