MFC r348885, r351543, r356806-r356807

r348885 by bz:
A bit of code hygiene (no functional changes).

Hide unused code under #ifdef notyet (in one case the only caller is under
that same ifdef), or if it is arm (not arm64) specific code under the
arm ifdef to not yield -Wunused-function warnings during the arm64
kernel compile.

r351543 by mmel:
Add support for RK3288 into existing RockChip drivers.
This patch ensures only minimal level of compatibility necessary to boot
on RK3288 based boards. GPIO and pinctrl interaction, missing in current
implementation, will be improved by own patch in the near future.

MFC with: r351452

r356806:
fdt_pinctrl: Add new methods for gpios

Most of the gpio controller cannot configure or get the configuration
of the pin muxing as it's usually handled in the pinctrl driver.
But they can know what is the pinmuxing driver either because they are
child of it or via the gpio-range property.
Add some new methods to fdt_pinctrl that a pin controller can implement.
Some methods are :
fdt_pinctrl_is_gpio: Use to know if the pin in the gpio mode
fdt_pinctrl_set_flags: Set the flags of the pin (pullup/pulldown etc ...)
fdt_pinctrl_get_flags: Get the flags of the pin (pullup/pulldown etc ...)

The defaults method returns EOPNOTSUPP.

Reviewed by: ian, bcr (manpages)
Differential Revision: https://reviews.freebsd.org/D23093

r356807:
arm64: rockchip: Add new interface for rk_pinctrl

The gpio controller in rockchips SoC in a child of the pinctrl driver
and cannot control pullups and pulldowns.
Use the new fdt_pinctrl interface for accessing pin capabilities and
setting them.
We can now report that every pins is capable of being IN or OUT function
and PULLUP PULLDOWN.
If the pin isn't in gpio mode no changes will be allowed.

Reviewed by: ganbold (previous version)
Differential Revision: https://reviews.freebsd.org/D22849