arm: socfpga: Move wrappers into platform directory

Move the wrappers for QTS-generated files into platform directory
out of the board directory. The trick here is to add -I to CFLAGS
such that it points to the board directory in source tree and thus
the qts/ directory there is still reachable.

Signed-off-by: Marek Vasut <marex@denx.de>