msm: smd_tty: fix missing open_timeout attribute

When systems are configured using device tree, the open timeout device
attribute is not created.

Move device attribute creation code to common device init function.

CRs-Fixed: 540229
Change-Id: I36e41d41857547a31650f87d6cd07fae8b58d750
Signed-off-by: Eric Holmberg <eholmber@codeaurora.org>