kingst-la2016: rephrase USB renum code path after firmware upload
The dev_open() routine postprocesses USB renumeration after a previous
FX2 MCU firmware upload. Concentrate all tunables in the driver's header
file, and discuss their meaning in relation to each other. Rephrase the
logic to start checking earlier, and keep checking for longer, adjust
diagnostics in the process. Void the "firmware uploaded" flag when the
upload took effect. Consistently use u64 for timestamps. Rename a few
variables to improve readabilty.