msm: ipc: Make the kernel-space read operation as non-blocking

Update the read operations of kernel space to be non-blocking and
return -ENOMSG when there is no message to read.

Change-Id: I92f55d8829755078f34ff3cbe2dc9b16ed7988df
Signed-off-by: Zaheerulla Meer <zmeer@codeaurora.org>