Added new drivers for isl29023.c made by Freescale.
Use new Freescale isl29023 driver in board-chagall-sensors.c.

Configure isl29023 driver to poll every 300 msec and generate an input event.
New read-only sysfs endpoints: mode_available, resolution_available, range_available enabling the user to see the capabilities of the device.

Changed existing sysfs endpoints for resolution and range to output and accept the real-world values instead of indices.
Changed external scaling resistor of isl29023 light sensor to the correct 499kOhm for chagall tegra board.
Changed interface for acquiring measurments: _show_lux measures ambient light with human spectral response. _show_ir measures light with an IR-heavy spectral sensitivity.

Measurements are now correctly triggered upon call to get_*_value by setting the correct mode.

Conversion of the ADC value to the real-world value in lux units is now done in a seperate function _convert_lux.
Changed default initialization values to 16-bit ADC (only this setting has 50/60 Hz flicker rejection).

Default mode is now defined by ISL29023_DEFAULT_MODE. The _set_power_state call in init is obsolete as the power state corresponds to a given mode.
Upon power-down as requested per set_power_state the previous mode is stored and reset correctly if the device is woken per set_power_state again.
The input device's maximum value is now set to the maximum gain range.
Implemented dynamic range selection to increase resoltution in case of lower light conditions.