leds: support new LP8501 device - another LP55xx common

leds: support new LP8501 device - another LP55xx common

LP8501 can drive up to 9 channels like LP5523.
LEDs can be controlled directly via the I2C and programmable engines are
supported.

LP55xx common driver
 LP8501 is one of LP55xx family device, so LP55xx common code are used.
 Chip specific data is defined in the structure, 'lp55xx_device_config'.

Differences between LP8501 and LP5523
 Different register layout for LED output control and others.
 LP8501 specific feature for separate output power selection.
 LP8501 doesn't support external clock detection.
 Different programming engine data.

LP8501 specific feature - output power selection
 Output channels are selected by power selection - Vout or Vdd.
 Separate power for VDD1-6 and VDD7-9 are available.
 It is configurable in the platform data.
 To support this feature, LP55xx DT structure and header are changed.
 Device tree binding is updated as well.

LED pattern data
 Example pattern data is updated in the driver documentation.

Signed-off-by: Milo Kim <milo.kim@ti.com>
Signed-off-by: Bryan Wu <cooloney@gmail.com>