media: i2c: ds90ub953: Restructure clkout management

Separate clkout calculations and register writes into two functions:
ub953_calc_clkout_params and ub953_write_clkout_regs, and add a struct
ub953_clkout_data that is used to store the clkout parameters.

This simplifies the clkout management.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>