drivers/leds: add driver for PCA9633 I2C chip

Driver for the PCA9633 I2C chip supporting four LEDs and 255 brightness
levels.

[akpm@linux-foundation.org: fix kcalloc() call]
[axel.lin@gmail.com: fix kcalloc parameters swapped]
Signed-off-by: Peter Meerwald <p.meerwald@bct-electronic.com>
Signed-off-by: Axel Lin <axel.lin@gmail.com>
Cc: Lars-Peter Clausen <lars@metafoo.de>
Cc: Richard Purdie <rpurdie@rpsys.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>