ARM dts: msm: DT changes to enable retention

Retention modes for testing only. The actual modes supported
would be a subset of these modes

CRS-fixed:975790
Change-Id: Ida27125d337f2a15ac152f49a14bdde254d3e535
Signed-off-by: Mahesh Sivasubramanian <msivasub@codeaurora.org>