Proper support for more sensor parameters of GC0308 (#814)

* gc0308: add proper support for sensor image and effect settings

This includes contrast, brightness, saturation, sharpness,
white-balance, gain & exposure levels and special effects.

* gc0308: read current setting values on sensor initialization

* gc0308: fix incomplete error handling and use defined values

* gc0308: fix sensor setting registers, defaults and setters

Brightness is not supported, but AEC value can be used.

* gc0308: update sensor defaults according to Linux kernel driver

Author: mback2k