greybus: power_supply: rework and operation changes

This is a major rework and changes to the current implementation of the
battery protocol. The previous implementation lack the support of a more
dynamic handle of power supply properties and updating of status. Also,
reflect the actual state of the greybus specification

So, with this new approach a set of operations to fetch the battery
module configuration and properties is add, new methods to cache and
update the values of properties, new operation to set properties if
declared writable and an event operation that can be triggered by the
module to force an update read on the properties values.

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