drivers: ieee802154: b91: add missing PLIC include

Driver was using RISC-V PLIC API without including the necessary
headers.

Signed-off-by: Gerard Marull-Paretas <[email protected]>

Author: gmarull

drivers/ieee802154/ieee802154_b91.c

@@ -26,6 +26,8 @@ LOG_MODULE_REGISTER(LOG_MODULE_NAME);
 #include <zephyr/net/openthread.h>
 #endif
 
+#include <zephyr/drivers/interrupt_controller/riscv_plic.h>
+
 #include "ieee802154_b91.h"