HID: logitech-hidpp: add support for Unified Battery (1004) feature

This new feature present in new devices replaces the old Battery Level Status
(0x1000) feature. It keeps essentially the same information for levels
(reporting critical, low, good and full) but makes these levels optional, the
device exports a capability setting which describes which levels it supports.
In addition to this, there is an optional state_of_charge paramenter that
exports the battery percentage.

This patch adds support for this new feature. There were some implementation
choices, as described below and in the code.

If the device supports the state_of_charge parameter, we will just export the
battery percentage and not the levels, which the device might still support.

Since this feature can co-exist with the Battery Voltage (0x1001) feature and
we currently only support one battery feature, I changed the battery feature
discovery to try to use 0x1000 and 0x1004 first and only then 0x1001, the
battery voltage feature.

In the future we could uncouple this and make the battery feature co-exists
with 0x1000 and 0x1004, allowing the device to export voltage information in
addition to the battery percentage or level.

I tested this patch with a MX Anywhere 3, which supports the new feature. Since
I don't have any device that doesn't support the state_of_charge parameter of
this feature, I forced the MX Anywhere 3 to use the level information, instead
of battery percentage, to test that part of the implementation.

I also tested with a MX Master 3, which supports the Battery Level Status
(0x1000) feature, and a G703 Hero, which supports the Battery Voltage (0x1001)
feature, to make sure nothing broke there.

[jkosina@suse.cz: fix comment]
Signed-off-by: Filipe Laíns <lains@archlinux.org>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>