include: include exception.h in fatal.h

`fatal.h` has 2 functions that use the `z_arch_esf_t` type.

Include `exception.h`, which should have the `z_arch_esf_t`
defined.

Signed-off-by: Yong Cong Sin <ycsin@meta.com>

include/zephyr/fatal.h

@@ -12,6 +12,7 @@
 #define ZEPHYR_INCLUDE_FATAL_H
 
 #include <zephyr/arch/cpu.h>
+#include <zephyr/arch/exception.h>
 #include <zephyr/toolchain.h>
 #include <zephyr/fatal_types.h>