diag: Prevent suspend while reading data from SMD and HSIC

Diag driver can let apps processor go to suspend when receiving
data from remote processors and peripherals. This can result in
diag data being dropped on the apps processor. This patch ensures
that the apps processor is awake till the data is copied to the
user space.

Change-Id: Id3c46c66675d3b5632721dede5e59420b69c568e
Signed-off-by: Ravi Aravamudhan <aravamud@codeaurora.org>