Move all declarations of free_initmem() to linux/mm.h

Move all declarations of free_initmem() to linux/mm.h so that there's only one
and it's used by everything.

Signed-off-by: David Howells <dhowells@redhat.com>
cc: linux-c6x-dev@linux-c6x.org
cc: microblaze-uclinux@itee.uq.edu.au
cc: linux-sh@vger.kernel.org
cc: sparclinux@vger.kernel.org
cc: x86@kernel.org
cc: linux-mm@kvack.org

arch/sh/include/asm/system.h

@@ -6,4 +6,3 @@
 #include <asm/exec.h>
 #include <asm/switch_to.h>
 #include <asm/traps.h>
-void free_initmem(void);