pinctrl: qcom: Introduce readl/writel accessors

In preparation for the support for dispersed tiles move all readl and
writel calls to helper functions. This will allow us to isolate the
added complexity of another indirection.

Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>