soc: qcom: hab: increase the maximum size of message

Previously, the supported maximum size of message sent
over hab was 4K bytes. Now, it is increased to 0xFFFF
bytes.

Change-Id: I3b539e42df2f5c5d3be4bbac7084adeb198c9a0b
Signed-off-by: Yong Ding <yongding@codeaurora.org>