MIPS: DTS: CI20: Enable support for WiFi / Bluetooth

Wire the WiFi/Bluetooth chip properly in the Device Tree.

- Provide it with the correct regulators and clocks;
- Change the MMC I/O bus to 1.8V which seems to be enough;
- Change the MMC I/O bus frequency to 25 MHz as 50 MHz causes errors;
- Fix the Bluetooth powerdown GPIO being inverted and add reset GPIO;
- Convert host-wakeup-gpios to IRQ.

With these changes, the WiFi works properly with the latest firmware
provided by linux-firmware. The Bluetooth does not work very well here,
as I cannot get my wireless keyboard to pair; but it does detect it, and
it does see the key presses when I type the pairing code.

Signed-off-by: Paul Cercueil <paul@crapouillou.net>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>