msm: ipa: add support to read EE from dts

Read and use the EE (execution environment) value assigned to
non-secure apps from the device tree. If the optional EE
property does not exist, a zero value for EE is assumed.

Change-Id: Idb9b8c43317fb0bfff5425aaaa840f7c2714f7f4
Signed-off-by: Ravi Gummadidala <rgummadi@codeaurora.org>