Mini Monitor 4K and Mini Recorder 4K are almost the same hardware with just changes on
the Video In/Out. For now tests have been done on the Mini Monitor 4K, but the aim  is
support both boards in the same platform/target in the future, thus the mini_4k naming.

These boards could be used as affordable Artix7 dev boards for LiteX, to run Linux with
LiteX (512MB of RAM + a Video Framebuffer) or to create custom systems like a fast software
defined signal generator/recorder directly from a PC over PCIe, custom HDMI/SDI video
cards, etc... lots of possibilities :)

Minor fixes for AU280 [work in progress]

terasic_sockit: fix: make video clock also optional as video terminal is optional

antmicro_lpddr4_test_board: fix ethernet rx delay issue

arty: add option to use litespi QSPI controller

Signed-off-by: Karol Gugala <kgugala@antmicro.com>

Signed-off-by: Karol Gugala <kgugala@antmicro.com>

Qmtech Wukong: updates

boards/compat: Skip targets with unsatisfied dependencies.

platforms/ecpix5: Add ULPI signals.

fix ethernet clock (it's a GMII), add FB support over the HDMI connector (hdmi clock set from the resolution)

Fixes #194

Add target for LPDDR4 Test Board

targets/digilent_nexys_video: Add specific Video PLL to give more flexibility on supported Video Timings.

- main_ram mem_map is now directly used by add_sdram when origin is None.
- max_sdram_size/min_l2_data_width are no longer exposed as targets arguments this can
still be used enforced directly in the few cases it is useful.