Enables build with angstrom-v2018.06-sumo

[feddischson]

This pull request contains multiple changes to enable angstrom-v2018.06-sumo on the de10-nano board.
In addition, two features are added:

• a minimal image is possible (with a smaller sdcard footprint)
• it is possible to provide a custom FPGA image (via local.conf)

Known open issues

• DMA in FFT_sub hangs de10-nano-hardware#4

Signed-off-by: Christian Haettich feddischson@gmail.com

[dwesterg]

Thanks. I will look over these.

[zeldin]

sumo is already EOL. I have extended this PR with initial support for thud and zeus in
feddischson/meta-de10-nano@master...zeldin:thud
and
feddischson/meta-de10-nano@master...zeldin:zeus
respectively. Probably needs a bit more work (like updating the README :) but it boots up and runs the LEDs demo at least...

Note that for zeus I needed to set ANGSTROM_GCC_VERSION ?= "arm-8.%" in local.conf, otherwise it tried to use version linaro-7.2, which is too old. Don't know why, I did update the linaro layer to zeus as well...