canbus: Move high-level CAN code to new src/generic/canbus.c

Separate out the high-level command processing logic from the
low-level transmission code.  Place the high-level code in
src/generic/canbus.c .

This also removes the CAN dependency on serial_irq.c .

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>

src/stm32/Kconfig

@@ -176,9 +176,9 @@ config CANSERIAL
     bool "Use CAN for communication (instead of serial)"
     depends on !USBSERIAL
     default n
-config SERIAL_BAUD
+config CANBUS_FREQUENCY
     int "CAN bus speed" if LOW_LEVEL_OPTIONS && CANSERIAL
-    default 500000 if CANSERIAL
+    default 500000
 choice
     depends on CANSERIAL
     prompt "CAN pins"