Debug commands should have deterministic toggle interface

[mithro]

From @deeprave on February 15, 2016 15:40

A feature request for the firmware to simplify and improve things a little:

Instead of the debug command being a toggle to the debug interface, be more deterministic and provide (even in addition to the toggle is ok):

debug [input]X [on|off]
and
debug [input]X ?

returning the current debug state for the selected channel, where X is 1 or 2.

In addition, missing value of 'X' should affect all available channels, and return status of all channels in the second case. e.g. "debug on" or "debug input on" should enable debug on all channels.

Copied from original issue: timvideos/HDMI2USB-firmware-prebuilt#3

[mithro]

@deeprave - To make this change the C code at https://github.com/timvideos/HDMI2USB-misoc-firmware/blob/master/firmware/lm32/ci.c#L629 should be modified.