OMAP: DSS2: Handle dpll4_m4_ck in dss_get/put_clocks

Get and put for dpll4_m4_ck was handled in dss_init/dss_exit. Move the
code to dss_get/put_clocks(), which is a better place to handle it.

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