buildroot

boards: add roseapple pi board support

Add basic support for the roseapple pi board, a SBC in a RPI form factor
with an Actions Semiconductor S500 SoC. For details, see:

http://roseapplepi.org/

The vendor kernel unfortunately needs a minor patch to build the XHCI
driver, so include it here.

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>