dt-binding: power: Add Qualcomm SMBB binding

Add the Qualcomm Switch-Mode Battery Charger and Boost device tree
binding.

Signed-off-by: Courtney Cavin <courtney.cavin@sonymobile.com>
Signed-off-by: Bjorn Andersson <bjorn.andersson@sonymobile.com>
Signed-off-by: Sebastian Reichel <sre@kernel.org>