Initial pinctrl driver for QCOM msm8994 platforms.

In order to continue the initial board support for QCOM msm8994/msm8992
presented in patches from Jeremy McNicoll <jeremymc@redhat.com>, let's put
a proper pinctrl driver in place.

Currently, the DT for these platforms uses the msm8x74 pinctrl driver to
enable basic UART.  Beyond the first few pins the rest are different enough
to justify it's own driver.

Note: This driver is also used by QCOM's msm8992 platform as it's TLM block
is the same.

- Initial formatting and style was taken from the msm8x74 pinctrl driver
  added by Björn Andersson <bjorn.andersson@linaro.org>
- Data was then adjusted per QCOM MSM8994v2 documentation for Top Level
  Multiplexing
- Bindings documentation was based on qcom,msm8996-pinctrl.txt by
  Joonwoo Park <joonwoop@codeaurora.org> and then modified for msm8994
  content
Signed-off-by: Michael Scott <michael.scott@linaro.org>
Tested-by: Jeremy McNicoll <jeremymc@redhat.com>
Acked-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>