ARM: dts: msm: Add cooling device property to charger in pm660

Add cooling-cells property to pm660 charger. This enables the charger
cooling device to be referenced in a thermal zone definition.

Change-Id: I49b36f09bba115408e7b02069a78abc4780c724b
Signed-off-by: Manaf Meethalavalappu Pallikunhi <manafm@codeaurora.org>