hexagon: switch over to generic free_initmem()

hexagon implementation of free_initmem() is currently empty and marked
with comment

 * Todo:  free pages between __init_begin and __init_end; possibly
 * some devtree related stuff as well.

Switch it to the generic implementation.

Link: http://lkml.kernel.org/r/1550515285-17446-3-git-send-email-rppt@linux.ibm.comSigned-off-by: Mike Rapoport <rppt@linux.ibm.com>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Palmer Dabbelt <palmer@sifive.com>
Cc: Richard Kuo <rkuo@codeaurora.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

arch/hexagon/mm/init.c

@@ -84,16 +84,6 @@ void __init mem_init(void)
 	init_mm.context.ptbase = __pa(init_mm.pgd);
 }
 
-/*
- * free_initmem - frees memory used by stuff declared with __init
- *
- * Todo:  free pages between __init_begin and __init_end; possibly
- * some devtree related stuff as well.
- */
-void __ref free_initmem(void)
-{
-}
-
 /*
  * free_initrd_mem - frees...  initrd memory.
  * @start - start of init memory