dt-bindings: mfd: pm8008: Add bindings

Add bindings for the Qualcomm Technologies, Inc. PM8008 MFD driver.

Signed-off-by: Guru Das Srinagesh <gurus@codeaurora.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>