qiprog: Allow specifying a chip read, write, or verify operation

Signed-off-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>
qiprog: Only stress test device if specified via cmdline option

qiprog (the application) should not do things on its own. The device test
code is useful for seeing if something may be wrong with the device, but
should not be run unless explicitly requested. Hence, only run it if
"-t | --test" is given as an argument.

Signed-off-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>