power: supply: PCHG: Peripheral device charger

This patch adds a driver for PCHG (Peripheral CHarGer). PCHG is a
framework managing power supplies for peripheral devices.

This driver creates a sysfs node for each peripheral charge port:

	/sys/class/power_supply/peripheral<n>

where <n> is the index of a charge port.

For example, when a stylus is connected to a NFC/WLC port, the node
returns:

	/sys/class/power_supply/peripheral0/
		capacity=50
		charge_type=Standard
		scope=Device
		status=Charging
		type=Battery

Signed-off-by: Daisuke Nojiri <dnojiri@chromium.org>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>