stm32f429i-disco: implements lcd initializing

This enables the initializing of the lcd device connected on the
stm32f429i-disco. The following methods are provided:
- up_lcdinitialize
- up_lcduninitialize
- up_lcdgetdev

The corresponding ili9341 lcd device in the nuttx driver section can be
configured by Kconfig. Interface 0 is used by default.

Signed-off-by: Marco Krahl <ocram.lhark@gmail.com>