Add support for QMTech 10CL006 board

rz_easyfpga: cleanup and ease of use

- update README
- delete some unnecessary toolchain commands (copied from trenz boards)
- use minimal cpu_variant by default when vexriscv is selected

Untested.

Compiles but untested on hardware.

Allows building bare metal demo and running it directly on these boards.

Wukong board improvements

This adds support for v2 of the board via a --board-version argument
and a way to select the FPGA speed grade via a --speed-grade argument.

Note that the speed grade now defaults to -1. QMTech confirmed that
V1 of the board were made in two batches, one with -1 and one with -2,
while V2 of the board is all -1. So -1 is the safer default.

This also fixes the inversion of j10 and j11 and a typo in the pin
definition of jp3

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

Initial Digilent Atlys support

Build tested with ./digilent_atlys.py --with-ethernet --build.

rz_easyfpga: adjust SDRAM clk phase, also add 1:2 rate

- also add 1:2 rate

With colorbars for now, need to free up BRAMS for Video Terminal (or finish HyperRAM support).

sipeed_tang_nano: Add SPI Flash, Enable CPU and use new external SPI Flash support from OpenFPGALoader.

./sipeed_tang_nano_4k.py --cpu-type=vexriscv --cpu-variant=lite --build --flash

        __   _ __      _  __
       / /  (_) /____ | |/_/
      / /__/ / __/ -_)>  <
     /____/_/\__/\__/_/|_|
   Build your hardware, easily!

 (c) Copyright 2012-2021 Enjoy-Digital
 (c) Copyright 2007-2015 M-Labs

 BIOS built on Sep 17 2021 15:54:08
 BIOS CRC passed (6cc6de6d)

 Migen git sha1: a5bc262
 LiteX git sha1: 46cd9c5a

--=============== SoC ==================--
CPU:		VexRiscv_Lite @ 27MHz
BUS:		WISHBONE 32-bit @ 4GiB
CSR:		32-bit data
ROM:		64KiB
SRAM:		8KiB
FLASH:		4096KiB

--========== Initialization ============--

Initializing W25Q32 SPI Flash @0x80000000...
SPI Flash clk configured to 13 MHz
Memspeed at 0x80000000 (Sequential, 4.0KiB)...
   Read speed: 1.3MiB/s
Memspeed at 0x80000000 (Random, 4.0KiB)...
   Read speed: 521.9KiB/s

--============== Boot ==================--
Booting from serial...
Press Q or ESC to abort boot completely.
sL5DdSMmkekro
Timeout
No boot medium found

--============= Console ================--

litex>