misc: led: Add PCA9551 LED driver

This patch adds a driver for the PCA9551 LED controller.

Originated-by: Timo Herbrecher <t.herbrecher@gateware.de>
Signed-off-by: Stefan Roese <sr@denx.de>
Reviewed-by: Tom Rini <trini@konsulko.com>
Cc: Fabio Estevam <festevam@gmail.com>
Reviewed-by: Fabio Estevam <fabio.estevam@freescale.com>