kdb: include kdb_private.h for function prototypes

The kdb_kbd_cleanup_state() is called from another file through
the kdb_private.h file, but that is not included before the
definition, causing a W=1 warning:

kernel/debug/kdb/kdb_keyboard.c:198:6: error: no previous prototype for 'kdb_kbd_cleanup_state' [-Werror=missing-prototypes]
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Link: https://lore.kernel.org/r/20230517124802.929751-1-arnd@kernel.orgSigned-off-by: Daniel Thompson <daniel.thompson@linaro.org>

kernel/debug/kdb/kdb_keyboard.c

@@ -13,6 +13,8 @@
 #include <linux/ctype.h>
 #include <linux/io.h>
 
+#include "kdb_private.h"
+
 /* Keyboard Controller Registers on normal PCs. */
 
 #define KBD_STATUS_REG		0x64	/* Status register (R) */