mfd: intel_soc_pmic_bxtwc: Add bxt_wcove_usbc device

The Intel Whiskey Cove PMIC includes several function units, e.g.
ADC, thermal, USB Type-C, GPIO, etc. The corresponding device has
to be created in the mfd driver(intel_soc_pmic_bxtwc.c). This change
adds the USB Type-c device.

Signed-off-by: Bin Gao <bin.gao@intel.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>