x86: tangier: Add initial ACPI support for PMIC device

Basin Cove PMIC is connected to I2C0 bus which is hidden from the OS
and access is going via SCU device, enumerated via PCI.

For now, we add just a minimum support of PMIC device to allow enabling,
e.g. USB OTG, in the OS.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Acked-by: Bin Meng <bmeng.cn@gmail.com>