dt: Document Qualcomm IPQ8064 pinctrl binding

Define a new binding for the Qualcomm TLMMv2 based pin controller inside the
IPQ8064.

Signed-off-by: Andy Gross <agross@codeaurora.org>
Reviewed-by: Bjorn Andersson <bjorn.andersson@sonymobile.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>