pcengines/apu2: add board support

Initial work based on db-ft3b-ls and code released by Eltan. Board
boots with some limitation.

Now the AGESA binary is harcoded and board specific until it's fixed
by the SoC vendor.

memtest86+ from external repo skips looking for SPD on SMBus, which when
performed cause memtest86+ to hang. Still didn't tried whole test suit.

SeaBIOS 1.9.3 have some problems with USB which lead to no booting in
some cases. Full log:
https://gist.github.com/pietrushnic/787cbf63f610ff4f6b4ac13e5c20b872

SeaBIOS from PC Engines repository (https://github.com/pcengines/seabios)
works fine. Those changes are planned for upstream.

Information about obtaining and booting Voyage Linux:
https://github.com/pcengines/apu2-documentation#building-firmware-using-apu2-image-builder

Change-Id: Id23e448e27f4bba47b7e9e7fa7679e2690c6e4bc
Signed-off-by: Piotr Król <piotr.krol@3mdeb.com>
Signed-off-by: Philipp Deppenwiese <zaolin@das-labor.org>
Reviewed-on: https://review.coreboot.org/14138
Tested-by: build bot (Jenkins)
Reviewed-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
26 files changed