soc: riscv: privilege: gd32vf103: undefine CAN_MODE_NORMAL

The GigaDevice HAL defines CAN_MODE_NORMAL, which conflicts with the
zephyr/drivers/can.h header definition. Undefine it in soc.h.

Fixes: #45611

Signed-off-by: Henrik Brix Andersen <hebad@vestas.com>

soc/riscv/riscv-privilege/gd32vf103/soc.h

@@ -21,6 +21,10 @@
 #ifndef _ASMLANGUAGE
 #include <zephyr/toolchain.h>
 #include <gd32vf103.h>
+
+/* The GigaDevice HAL headers define this, but it conflicts with the Zephyr can.h */
+#undef CAN_MODE_NORMAL
+
 #endif  /* !_ASMLANGUAGE */
 
 #endif  /* RISCV_GD32VF103_SOC_H */