Add sample application for NXP PCA9633 LED driver. This application
test the 4 LEDs by doing the following:
- turn on LEDs
- turn off LEDs
- set the brightness to 50%
- turn off LEDs
- blink the LEDs
- turn off LEDs
The application is based on the stm32373_eval board and expects to have
a PCA9633 LED driver on the bus I2C-1 at the address 0x62.
Signed-off-by: Sebastien Bourdelin <sebastien.bourdelin@savoirfairelinux.com>