ARM: dts: msm: enable real time priority for SPI bus on MSM8939

SPI bus at channel number 5 is used to transmit real time touch
screen data. Therefore, high priority of message pump from queue
is needed to make sure of good user performance.

Change-Id: I8732739bbf193f01c7db08ea5e49bd4d90233137
Signed-off-by: Chun Zhang <chunz@codeaurora.org>