Fix Split keyboards so they compile on Configurator (#3051)

* Fix serial split for BFO9000

* Fix serial split for DeltaSplit75

* Fix serial split for Helix

* Fix serial split for MiniDox

* Fix serial split for Viterbi

* Revert "Fix serial split for Helix" since it's super complex

This reverts commit 72538df105.

We'll let the helix owner fix this issue, or dive into the code later

keyboards/bfo9000/serial.c

@@ -12,7 +12,7 @@
 #include <stdbool.h>
 #include "serial.h"
 
-#ifdef USE_SERIAL
+#ifndef USE_I2C
 
 // Serial pulse period in microseconds. Its probably a bad idea to lower this
 // value.

keyboards/deltasplit75/serial.c

@@ -12,7 +12,7 @@
 #include <stdbool.h>
 #include "serial.h"
 
-#ifdef USE_SERIAL
+#ifndef USE_I2C
 
 // Serial pulse period in microseconds. Its probably a bad idea to lower this
 // value.

keyboards/minidox/serial.c

@@ -12,7 +12,7 @@
 #include <stdbool.h>
 #include "serial.h"
 
-#ifdef USE_SERIAL
+#ifndef USE_I2C
 
 // Serial pulse period in microseconds. Its probably a bad idea to lower this
 // value.

keyboards/viterbi/serial.c

@@ -12,7 +12,7 @@
 #include <stdbool.h>
 #include "serial.h"
 
-#ifdef USE_SERIAL
+#ifndef USE_I2C
 
 // Serial pulse period in microseconds. Its probably a bad idea to lower this
 // value.