[Keyboard] KBD75 refactor (#6755)

[Keyboard] KBD75 refactor (#6755)

* convert codebase to #pragma once

* fix file includes

- quantum.h is included at keyboard level, redundant at revision level
- keyboard-level path is accessible at revision level, remove relative pathing

* duplicate common layout macros from rev1 to rev2

Add the layout macros supported by both rev1 and rev2 to rev2.h directly, which exposes these layouts to QMK Configurator.

* enable community layout support (75_ansi, 75_iso)

* add LAYOUT_75_iso layout data

It needs its own tree because its keys are in a different order from LAYOUT_iso_1u even though the physical layout is the same.

* minimize rules.mk files (use QMK defaults)

* use atmel-dfu bootloader rule

* fix typo on rev1 info.json