modem: pipe: Add explicit timeout to sync APIs

The modem pipe APIs include synchronous calls to open/close,
which internally use a fixed timeout of 10 seconds. The timeout
should be configurable through the APIs, anywhere from K_NO_WAIT
to K_FOREVER.

This commit adds timeout parameters to the open/close APIs, and
updates in-tree usage of the open/close APIs to explicitly
provide the previously implicit timeout of 10 seconds.

Signed-off-by: Bjarki Arge Andreasen <bjarki@arge-andreasen.me>