mfd: Add support for Qualcomm SPMI PMICs

The Qualcomm SPMI PMIC chips are components used with the
Snapdragon 800 series SoC family.  This driver exists
largely as a glue mfd component, it exists to be an owner
of an SPMI regmap for children devices described in
device tree.

Signed-off-by: Josh Cartwright <joshc@codeaurora.org>
Signed-off-by: Stanimir Varbanov <svarbanov@mm-sol.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>