RFC: applet.program.ecp5_flash

[gregdavill]

This is my initial work at using the spi_background_programming mode of the Lattice ECP5 FPGA to perform operations on the configuration memory via JTAG, instead of requiring a separate SPI connection.

This code builds on the work of #191

This applet is essentially a wrapper for memory.25x which overrides _command() with one that sends commands over JTAG instead of SPI.

I've been successful with getting this to work on some ECP5 boards here, but still has a few features that I'd like to add.

greg@xps:~/projects/Glasgow/software$ glasgow run program-ecp5-flash --pin-tck 3 --pin-tms 2 --pin-tdi 0 --pin-tdo 1 --freq 6000 --voltage 3.3 identify
I: g.device.hardware: device already has bitstream ID e7f22a6221689b598c39f770500c31ca
I: g.cli: running handler for applet 'program-ecp5-flash'
I: g.applet.program.ecp5_flash: port(s) A, B voltage set to 3.3 V
I: g.applet.program.ecp5_flash: manufacturer=0x021 (Lattice Semi.) part=0x1112 version=0x4
I: g.applet.program.ecp5_flash: Found Device: ECP5Device(name='LFE5U-45', idcode=1091641411)
I: g.applet.memory.25x: JEDEC manufacturer 0x01 (AMD) device 0x17 (8-bit ID)
I: g.applet.memory.25x: JEDEC manufacturer 0x01 (AMD) device 0x2018 (16-bit ID)
I: g.applet.memory.25x: device has valid SFDP 1.6 (JESD216B) descriptor
I: g.applet.memory.25x:   SFDP table #0: JEDEC, Flash Parameter Table 1.0 (JESD216)
I: g.applet.memory.25x:     density (Mbits)        : 128
...

[whitequark]

This applet is a bit hard to review--I think I'll be able to give it a full review after #191. That said, it needs to be updated to track latest changes in Glasgow too.