alpha: fix build failures

BugLink: http://bugs.launchpad.net/bugs/1745054

commit 8ee912da upstream.

The build of alpha allmodconfig is giving error:

  arch/alpha/include/asm/mmu_context.h: In function 'ev5_switch_mm':
  arch/alpha/include/asm/mmu_context.h:160:2: error:
	implicit declaration of function 'task_thread_info';
	did you mean 'init_thread_info'? [-Werror=implicit-function-declaration]

The file 'mmu_context.h' needed an extra header file.

Link: http://lkml.kernel.org/r/1505668810-7497-1-git-send-email-sudipm.mukherjee@gmail.comSigned-off-by: Sudip Mukherjee <sudipm.mukherjee@gmail.com>
Cc: Richard Henderson <rth@twiddle.net>
Cc: Ivan Kokshaysky <ink@jurassic.park.msu.ru>
Cc: Matt Turner <mattst88@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>

arch/alpha/include/asm/mmu_context.h

@@ -7,6 +7,7 @@
  * Copyright (C) 1996, Linus Torvalds
  */
 
+#include <linux/sched.h>
 #include <asm/machvec.h>
 #include <asm/compiler.h>
 #include <asm-generic/mm_hooks.h>