stm32f429i-disco: Add support for initializing ltdc framebuffer and the configured lcd display

This adds support for initializing of the ltdc controller and the lcd device connected on the stm32f429i-disco. The following methods are provided for the generic fb interface:

- up_fbinitialize
- up_fbgetvplane
- fb_uninitialize

The following methods are provided for the ltdc interface:

- up_ltdcgetlayer

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