Initial import of Ralink/Mediatek MIPS SoC support #2

This revision adds the following to the Mediatek/Ralink support:

• initial support for "clocks" FDT property, currently based on fdt_clock
• initial support for "resets" FDT property, currently based on the fdt_reset interface from D5826
• initial support for "pinctrl,bits" functionality via FDT. May be extended in the future to cover a better and fuller pinctrl implementation

Approved by: adrian (mentor)
Sponsored by: Smartcom - Bulgaria AD
Differential Revision: https://reviews.freebsd.org/D5827