media: si2157: module debug option to wait on signal lock

In some debugging cases it is useful to know how long it took
signal lock to happen after tuning. This can help diagnose
line issues.

Signed-off-by: Brad Love <brad@nextdimension.cc>
Signed-off-by: Sean Young <sean@mess.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>