mips: kexec: include linux/reboot.h

Two functions are provided for kexec, but the mips implementation is
missing the corresponding #include statment:

arch/mips/kernel/machine_kexec.c:136:1: error: no previous prototype for 'machine_shutdown' [-Werror=missing-prototypes]
arch/mips/kernel/machine_kexec.c:152:1: error: no previous prototype for 'machine_crash_shutdown' [-Werror=missing-prototypes]

Link: https://lkml.kernel.org/r/20231204115710.2247097-21-arnd@kernel.orgSigned-off-by: Arnd Bergmann <arnd@arndb.de>
Cc: Stephen Rothwell <sfr@rothwell.id.au>
Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

arch/mips/kernel/machine_kexec.c

@@ -8,6 +8,7 @@
 #include <linux/mm.h>
 #include <linux/delay.h>
 #include <linux/libfdt.h>
+#include <linux/reboot.h>
 
 #include <asm/cacheflush.h>
 #include <asm/page.h>