Changes

gateware: Add a proper 'busy' indicator in capture hardware

This allows the software to know if we're currently inside a packet.

Note that when ctrl_active is set low a new packet can still start
a tiny bit after since we could be inside of receiving the SYNC or
PID byte and 'busy' will only enable after the first byte of the
packet.

Signed-off-by: Sylvain Munaut <tnt@246tNt.com>

firmware: Make sure we're not in a packet before starting flush mode

If we start flush mode inside a packet, then the data fifo could
become empty temporarely, triggering the auto-stop ... and then
fill a little bit again, messing up the flush sequence.

Signed-off-by: Sylvain Munaut <tnt@246tNt.com>

firmware: At the end of a flush, send either short packet or ZLP

To indicate to the host that the transfer is done and nothing else
is expected, we send either a short packet or a ZLP. Before a short
packet would be sent but if transfer happened to be a multiple of
packet size, then nothing would be sent afterward.

Signed-off-by: Sylvain Munaut <tnt@246tNt.com>

firmware/main: Disable console for non-debug builds

Avoid any accidental presses

Signed-off-by: Sylvain Munaut <tnt@246tNt.com>

firmware/main: Use defines for misc CSR

Signed-off-by: Sylvain Munaut <tnt@246tNt.com>

firmware/main: Cleanup start.S a bit and disable boot debug

Signed-off-by: Sylvain Munaut <tnt@246tNt.com>

firmware: Change cross compiler to riscv-none-elf-

Signed-off-by: Sylvain Munaut <tnt@246tNt.com>