ARM: dts: msm: Remove Mx retention support for MSM8996

Remove Mx retention support at low temperature
for MSM8996 since it is not required for this
target.

Change-Id: Ia7f4c2f20bd0d70e5e6ca46ae79514a3b36a9b46
Signed-off-by: Shiju Mathew <shijum@codeaurora.org>