rpmsg: qcom_smd: Add check for remote state in send api

Add support to check channel remote state while doing
a send. Added a wake_up_interruptible call to
unblock send api and release the mutex lock so that
channel close and reopen can happen gracefully.

Change-Id: Ifcf0dad1d9f9f4d4404d62920f1b9d2f1d45ba16
Signed-off-by: Vivek Golani <vgolani@codeaurora.org>