Common west flash, debug arguments like --hex-file can't be used from command line

[mbolivar]

Describe the bug
eb95bed broke the ability to west flash --hex-file foo.hex.

A fix is in #23171

To Reproduce
Steps to reproduce the behavior:

1. west build -b nrf52840_pca10056 -s samples/hello_world
2. cp build/zephyr/zephyr.hex my-cool-zephyr.hex
3. west flash --hex-file my-cool-zephyr.hex

Notice that build/zephyr/zephyr.hex is flashed, not my-cool-zephyr.hex.

Expected behavior
my-cool-zephyr.hex is flashed instead.

Impact
Showstopper

Environment (please complete the following information):

• Commit SHA or Version used: introduced in eb95bed

Additional context
Reported by Tarjei Knapstad on Slack.

[jhedberg]

#23171 was merged