Next set of split_common changes (#4974)

* Update split_common to use standard i2c drivers

* Eliminate RGB_DIRTY/BACKLIT_DIRTY

* Fix avr i2c_master error handling

* Fix i2c_slave addressing

* Remove unneeded timeout on i2c_stop()

* Fix RGB I2C transfers

* Remove incorrect comment

quantum/keymap_common.c

@@ -29,10 +29,6 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #include "backlight.h"
 #include "quantum.h"
 
-#ifdef SPLIT_KEYBOARD
-    #include "split_flags.h"
-#endif
-
 #ifdef MIDI_ENABLE
 	#include "process_midi.h"
 #endif
@@ -138,39 +134,21 @@ action_t action_for_key(uint8_t layer, keypos_t key)
     #ifdef BACKLIGHT_ENABLE
         case BL_ON:
             action.code = ACTION_BACKLIGHT_ON();
-            #ifdef SPLIT_KEYBOARD
-                BACKLIT_DIRTY = true;
-            #endif
             break;
         case BL_OFF:
             action.code = ACTION_BACKLIGHT_OFF();
-            #ifdef SPLIT_KEYBOARD
-                BACKLIT_DIRTY = true;
-            #endif
             break;
         case BL_DEC:
             action.code = ACTION_BACKLIGHT_DECREASE();
-            #ifdef SPLIT_KEYBOARD
-                BACKLIT_DIRTY = true;
-            #endif
             break;
         case BL_INC:
             action.code = ACTION_BACKLIGHT_INCREASE();
-            #ifdef SPLIT_KEYBOARD
-                BACKLIT_DIRTY = true;
-            #endif
             break;
         case BL_TOGG:
             action.code = ACTION_BACKLIGHT_TOGGLE();
-            #ifdef SPLIT_KEYBOARD
-                BACKLIT_DIRTY = true;
-            #endif
             break;
         case BL_STEP:
             action.code = ACTION_BACKLIGHT_STEP();
-            #ifdef SPLIT_KEYBOARD
-                BACKLIT_DIRTY = true;
-            #endif
             break;
     #endif
     #ifdef SWAP_HANDS_ENABLE