[RPI][SPLASH] enable splash screen on RaspberryPi
This merge request:
- patches U-boot to display the splash bmp from SD (splashsource)
- configures logo display with kernel cmdline args (fbcon)
- excludes bbappends
meta-raspberrypi/recipes-core/psplash/
to display edgehog logo instead of raspberry - configures some drivers as built-in kernel modules, otherwise psplash crashes and causes the OS to hang after boot