ARM: msm: dts: Add sleep-set configuration for LDO L7

Add sleep-set configuration for LDO L7 to allow it
to enter low-power-mode.

Change-Id: I166e139098ace2c56de8a21c0d0f5a8fb3e44091
Signed-off-by: Anirudh Ghayal <aghayal@codeaurora.org>