OMAPDSS: Remove dss_debug variable

All the debug prints have been replaced with pr_debug(). Thus, the dependency on
dss_debug variable is replaced with dyndbg in dynamic debugging mode and DEBUG
flag otherwise. So, the dss_debug variable is removed along with checks for
DEBUG flag.

Signed-off-by: Chandrabhanu Mahapatra <cmahapatra@ti.com>
Reviewed-by: Sumit Semwal <sumit.semwal@ti.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>