ARM: dts: msm: remove guard-memory region support for rmtfs on sm6150

Guard-memory WA support is not required for sm6150 as the target has
the fix for XPU limitation.

Change-Id: Ic753794c0ab5c11735edeed72e1cd60d288d5ec4
Signed-off-by: Ankit Jain <jankit@codeaurora.org>