OMAPDSS: DSI: remove unused hsdiv wait funcs

With the previous patch "OMAPDSS: DSI: wait for hsdiv clocks when
enabling PLL",  dsi_wait_pll_hsdiv_dispc_active and
dsi_wait_pll_hsdiv_dsi_active are no longer needed, so they and the
callers can be removed.

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