pinctrl: pinconf-generic: loose DT dependence

New pin controllers such as ACPI-based may also have custom properties
to parse, and should be able to use generic pin config. Let's make the
code compile on !OF systems and rename members a bit to underscore it
is custom parameters and not necessarily DT parameters.

This fixes a build regression for x86_64 on the zeroday kernel builds.

Reported-by: kbuild test robot <fengguang.wu@intel.com>
Reviewed-and-tested-by: Soren Brinkmann <soren.brinkmann@xilinx.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>