* 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
* Previous version of multiple overrides of the default value of ZMK_USB
were problematic. Move to using board _defconfig files for the
defaults for those, along with proper `depends on` for ZMK_USB that
accounts for split and split roles.
CONFIG_ZMK_BATTERY_NRF_VDDH and CONFIG_ZMK_BATTERY_VOLTAGE_DIVIDER are
now automatically enabled if a DT node with the matching "compatible"
property is present and enabled, so they no longer need to be manually
set for each board.