ARM - Initial backlight support (#6487)

* Move AVR backlight to own file, add borrowed ARM implementation

* Tiny fix for backlight custom logic

* Remove duplicate board from rebase

* Fix f303 onekey example

* clang-format

* clang-format

* Remove backlight keymap debug

* Initial pass of ARM backlight docs

* Initial pass of ARM backlight docs - resolve todos

* fix rules validation logic

* Add f072 warning

* Add f072 warning

* tidy up breathing in backlight keymap

* tidy up breathing in backlight keymap

* add missing break to backlight keymap

common_features.mk

@@ -229,19 +229,32 @@ ifeq ($(strip $(LCD_ENABLE)), yes)
     CIE1931_CURVE = yes
 endif
 
-ifeq ($(strip $(BACKLIGHT_ENABLE)), yes)
+# backward compat
+ifeq ($(strip $(BACKLIGHT_CUSTOM_DRIVER)), yes)
+    BACKLIGHT_ENABLE = custom
+endif
+
+VALID_BACKLIGHT_TYPES := yes custom
+
+BACKLIGHT_ENABLE ?= no
+ifneq ($(strip $(BACKLIGHT_ENABLE)), no)
+    ifeq ($(filter $(BACKLIGHT_ENABLE),$(VALID_BACKLIGHT_TYPES)),)
+        $(error BACKLIGHT_ENABLE="$(BACKLIGHT_ENABLE)" is not a valid backlight type)
+    endif
+
     ifeq ($(strip $(VISUALIZER_ENABLE)), yes)
         CIE1931_CURVE = yes
     endif
 
-
-    COMMON_VPATH += $(QUANTUM_DIR)/backlight
-    SRC += $(QUANTUM_DIR)/backlight/backlight.c
-    OPT_DEFS += -DBACKLIGHT_ENABLE
-
     ifeq ($(strip $(BACKLIGHT_ENABLE)), custom)
         OPT_DEFS += -DBACKLIGHT_CUSTOM_DRIVER
     endif
+
+    ifeq ($(PLATFORM),AVR)
+        SRC += $(QUANTUM_DIR)/backlight/backlight_avr.c
+    else
+        SRC += $(QUANTUM_DIR)/backlight/backlight_arm.c
+    endif
 endif
 
 VALID_WS2812_DRIVER_TYPES := bitbang pwm spi i2c