ARM: dts: msm: Add DDR52 support in eMMC for low scaling on 8937

This adds support to switch to DDR52 mode instead of HS mode
in low load conditions.

Change-Id: I63137a76c60adfdab91d8749c86336e269f09af8
Signed-off-by: Pavan Anamula <pavana@codeaurora.org>