WS2812 driver gateware for blinkenwall v3

At 100 FPS, a single strand of WS2812 can only be just over 300 LEDs long:

MAX_LENGTH = (1 / FPS - RESET_TIME) / BIT_TIME / BITS_PER_PIXEL
318 = (1 / 100 - 50e-6) / 1.3e-6 / 24

Because blinkenwall v3 has 64 * 96 = 6144 pixels, driving it at 100 FPS requires at least 6144 / 318 = 20 parallel drivers. For simplicity, the wall is devided into 24 strands of 256 LEDs. Unfortunately, most microcontrollers have at most a couple WS2812-capable interfaces (typically SPI), so this would require coordinating several microcontrollers in parallel. A much more integrated solution is to instantiate as many WS2812 drivers as desired in an FPGA, then point the entire video firehose at the FPGA.