mips: bmips: bcm63268: populate device tree nodes

- Rename periph_clk to periph_osc.
- Rename clkctl to periph_clk.
- Move syscon-reboot to subnode.
- Add hsspi-osc clock.
- Add watchdog.
- Add HS SPI controller
- Add NAND controller.
- Add USBH PHY.

Signed-off-by: Álvaro Fernández Rojas <noltari@gmail.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>