greybus: firmware: Improve test application

It can take arguments not and we can perform all the operations with a
single binary, sorry for missing that initially.

Usage: ./firmware <gb-fw-mgmt-X> <type: interface/backend> <firmware-tag> <timeout>

And all of them have default values, etc.

Tested with a semco 13 MP module.

Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>