misc: kgdbts: Display progress of asynchronous tests

misc: kgdbts: Display progress of asynchronous tests

kgdbts includes a couple of different "thrashing" style tests that
may have long runtimes (especially on simulated platforms) and which
run asynchronously. This is uncomfortable for interactive use and
makes setting timeouts tricky for automatic use.

Fix by providing a optional means to show progress during these tests.
Selecting 100 is somewhat arbitrary but it matches the step used on
the synchronous tests, is large enough to keep the call to printk
from invalidating the testing and is human enough to "feel about
right".

Signed-off-by: Daniel Thompson <daniel.thompson@linaro.org>
Signed-off-by: Jason Wessel <jason.wessel@windriver.com>