OMAPDSS: DISPC: Cleanup cpu_is_xxxx checks

All the cpu_is checks have been moved to dispc_init_features function providing
a much more generic and cleaner interface. The OMAP version and revision
specific functions and data are initialized by dispc_features structure which is
local to dispc.c.
Signed-off-by: Chandrabhanu Mahapatra <cmahapatra@ti.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>