MN10300: asm/uaccess.h needs to #include linux/kernel.h for might_sleep()

MN10300's asm/uaccess.h needs to #include linux/kernel.h to get might_sleep()
otherwise it fails to build on MN10300 allyesconfig.  This fails in a few
places with messages like the following:

  In file included from security/keys/trusted.c:14:
  include/linux/uaccess.h: In function '__copy_from_user_nocache':
  include/linux/uaccess.h:52: error: implicit declaration of function 'might_sleep'
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

arch/mn10300/include/asm/uaccess.h

@@ -15,6 +15,7 @@
  * User space memory access functions
  */
 #include <linux/thread_info.h>
+#include <linux/kernel.h>
 #include <asm/page.h>
 #include <asm/errno.h>