phy: cpcap-usb: Add CPCAP PMIC USB support

Some Motorola phones like droid 4 use a custom CPCAP PMIC that has a
multiplexing USB PHY.

This USB PHY can operate at least in four modes using pin multiplexing
and two control GPIOS:

- Pass through companion PHY for the SoC USB PHY
- ULPI PHY for the SoC
- Pass through USB for the modem
- UART debug console for the SoC

This patch adds support for droid 4 USB PHY and debug UART modes,
support for other modes can be added later on as needed.

Both peripheral and host mode are working for the USB. The
host mode depends on the cpcap-charger driver for VBUS.

VBUS and ID pin detection are done using cpcap-adc IIO ADC
driver.

Cc: devicetree@vger.kernel.org
Cc: Marcel Partap <mpartap@gmx.net>
Cc: Michael Scott <michael.scott@linaro.org>
Acked-by: Rob Herring <robh@kernel.org>
Tested-by: Sebastian Reichel <sre@kernel.org>
Signed-off-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>