OMAPDSS: DSI: separate LP clock info from dsi_clock_info

struct dsi_clock_info represents the clocks handled by the DSI, mostly
PLL related clocks. In an effort to create common PLL code, we need to
remove all the non-PLL items from dsi_clock_info.

This patch removes LP clock related fields from dsi_clock_info, and
creates a new struct dsi_lp_clock_info for holding clock info for the LP
clock.

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