applet: migrate to nmigen, fix coroutine-related issue.

applet.interface.i2c_target: fix test.

README: mention nRF24 stuff.

applet.radio.nrf24l01: fix monitor 1-byte CRC calculation. Also, unmark the applet as preview, since it seems good enough.

arch.nrf24l.rf: fix swapped CRCO and EN_CRC fields.

firmware: rename PIND_OEQ_N to PIND_OEQ_N_REVAB PIND_OEQ_N is only connected on revAB and left floating on revC. Rename the pin to better reflect this.

firmware, device.hardware, applet.internal.selftest: add comments re nOE lines only existing on revAB

applet.program.nrf24lx1: improve help text. NFC.

gateware.pads: fix misuse of Module.

applet.memory.24x: add verify operation.