target: socfpga: Add Altera SoCFPGA support

This patch adds support for the Altera SoCFPGA target.
Both generic target and Terasic SoCkit boards are supported.

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

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@49367 3c298f89-4303-0410-b956-a3cf2f4a3e73