mfd: intel_soc_pmic: Core driver

This patch provides the common I2C driver code for Intel SoC PMICs.

Signed-off-by: Yang, Bin <bin.yang@intel.com>
Signed-off-by: Zhu, Lejun <lejun.zhu@linux.intel.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>