* 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.
Adds support for the CKP family of boards
BT60V2 ANSIHotswap, ISO Hotswap, ANSI Lowpro and soldered
BT65 ANSI Hotswap, ISO Hotswap and soldered
BT75 ANSI Hotswap and soldered
The BT65 and BT75 are stylised as btXX_v1 in order to maintain compatibility with customers existing zmk-config setups in the same way the BT60 V1 was handled when merged into main.
CKP boards have identical pinmapping between hotswap and soldered so there's only one set of defconfig, dts, keymap, yaml and yml files per size
