greybus: power_supply: add missing defines present in the specification

Some of the Greybus properties values (capacity level and scope) even
though they are defined in the specification were missing from the
protocol header.

They still match the kernel ones, but they should be present in there
for protocol sake.

Signed-off-by: Rui Miguel Silva <rui.silva@linaro.org>
Reviewed-by: Sandeep Patil <sspatil@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>