Replace serial.c of quantum/split_common/ (#4669)

* Add provisional Helix implementation to test the quantum/split_common.

* copy keyboards/helix/serial.[ch] to quantum/split_common/

* Make serial.c a pure driver.

Remove buffer name and buffer size from serial.c. They should be placed in the caller(matrix.c, split_utils.c).

* remove quantum/split_common/serial_backward_compatibility.h

* Changed array serial_master_buffer to structure serial_m2s_buffer.

* Changed array serial_slave_buffer to structure serial_s2m_buffer.

* Change keyboards/miniaxe/matrix.c

I also made changes to quantum/split_comon/matrix.c to keyboards/miniaxe/matrix.c.

Note: I contacted @ka2hiro, creator of miniaxe, and I got permission to change keyboards/miniaxe/matrix.c.

* update history comment in quantum/split_common/serial.c

* Revert "Add provisional Helix implementation to test the quantum/split_common."

This reverts commit 168c82ef82c88e79979d9796bab9cc819cc2f685.

* fix keyboards/miniaxe/matrix.c, quantum/split_common/matrix.c

avr-gcc 4.9.[23] report error.
avr-gcc 5.4.0, avr-gcc 7.3.0 pass.
It is funny.

* update comment quantum/split_common/serial.c

* Reserve RGBLIGHT_SPLIT macro in quantum/split_common

1 files changed, 0 insertions, 5 deletions

diff --git a/common_features.mk b/common_features.mk
index 73aab5d84..883681324 100644
--- a/common_features.mk
+++ b/common_features.mk
@@ -263,11 +263,6 @@ ifneq ($(strip $(CUSTOM_MATRIX)), yes)
 endif
 
 ifeq ($(strip $(SPLIT_KEYBOARD)), yes)
-    SERIAL_BACKWARD_COMPAT := $(wildcard $(QUANTUM_DIR)/split_common/serial_backward_compatibility.h)
-    ifneq ($(SERIAL_BACKWARD_COMPAT),)
-      CONFIG_H += $(SERIAL_BACKWARD_COMPAT)
-      # $(info CONFIG_H=$(CONFIG_H))
-    endif
     OPT_DEFS += -DSPLIT_KEYBOARD
     QUANTUM_SRC += $(QUANTUM_DIR)/split_common/split_flags.c \
                 $(QUANTUM_DIR)/split_common/split_util.c