feat(boards): Update for mikoto board definition (#1946)

* Set default revision to 5.20
* update mikoto board defs
* add revision info to mikoto.zmk.yml
* use zephyr aliases to handle mikoto_520
* enable pull-ups for on-board i2c

app/boards/arm/mikoto/mikoto.yaml

@@ -0,0 +1,15 @@
+identifier: mikoto
+name: mikoto
+type: mcu
+arch: arm
+toolchain:
+  - zephyr
+  - gnuarmemb
+  - xtools
+supported:
+  - adc
+  - usb_device
+  - ble
+  - ieee802154
+  - pwm
+  - watchdog