ARM: dts: msm: Add shared_ee property to bg spi node

Add shared_ee property for bg spi node. It helps to have the
spi as a shared resource with TZ.

Change-Id: I2a2c36783b4222fe1fcff7dba7e5f80281ce1184
Signed-off-by: Ajit Kumar <kajit@codeaurora.org>