Remove the need to specify NUM_OF_ENCODERS for the Encoder feature (#6328)

* Remove the need to set NUM_OF_ENCODERS

Instead, calculate the size of the array, and use that instead

* Add hack for split common support

* Remove NUM_OF_ENCODERS from keyboard config

Can be reverted, if needed

quantum/split_common/transport.c

@@ -17,6 +17,8 @@
 
 #ifdef ENCODER_ENABLE
 #  include "encoder.h"
+static pin_t encoders_pad[] = ENCODERS_PAD_A;
+#  define NUMBER_OF_ENCODERS (sizeof(encoders_pad)/sizeof(pin_t))
 #endif
 
 #if defined(USE_I2C) || defined(EH)