pinctrl-snapdragon: Get rid of custom drive-strength values

Use standard pinconf drive-strength values from Linux DT bindings rather
than ones based on custom u-boot header. These changes are in direction
to make u-boot DTs for Qcom SoCs to be compatible with standard Linux
DT bindings.

Also, add support for pinconf bias-pull-up.

Signed-off-by: Sumit Garg <sumit.garg@linaro.org>