LEDS: add BlinkM RGB LED driver, documentation and update MAINTAINERS

Add driver for BlinkM device to drivers/leds/.
Add entry to MAINTAINERS file.
Add documentation in Documentation/leds/.

A BlinkM is a RGB LED controlled through I2C.

This driver implements an interface to the LED framework
and another sysfs group to access the internal options
of the BlinkM.

rev6: Use module_i2c_driver().
rev5: Removed own workqueue in favor of events wq.
rev4: Fixed comments by Bryan Wu.
rev3: Fixed issues found by Jonathan Neuschäfer.

(bryan.wu@canonical.com: remove 2 trailing whitespace)

Signed-off-by: Jan-Simon Möller <jansimon.moeller@gmx.de>
Signed-off-by: Bryan Wu <bryan.wu@canonical.com>