Make configure_overlay() and configure_manager() take overlay/manager
pointer as an argument, instead of the ovl/mgr id. This will be useful
with the future patches.

Also rename the functions to be a bit more informative:
dss_ovl_write_regs, dss_mgr_write_regs, dss_write_regs.
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>