dt-bindings: power: Convert bq27xxx dt to yaml

Convert the bq27xxx.txt to yaml format

CC: Pali Rohár <pali@kernel.org>
CC: Andrew F. Davis <afd@ti.com>
Signed-off-by: Dan Murphy <dmurphy@ti.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>