riscv: switch over to generic free_initmem()

The riscv version of free_initmem() differs from the generic one only in
that it sets the freed memory to zero.

Make ricsv use the generic version and poison the freed memory.

Link: http://lkml.kernel.org/r/1550515285-17446-5-git-send-email-rppt@linux.ibm.comSigned-off-by: Mike Rapoport <rppt@linux.ibm.com>
Reviewed-by: Palmer Dabbelt <palmer@sifive.com>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Christoph Hellwig <hch@lst.de>
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/riscv/mm/init.c

@@ -66,11 +66,6 @@ void __init mem_init(void)
 	mem_init_print_info(NULL);
 }
 
-void free_initmem(void)
-{
-	free_initmem_default(0);
-}
-
 #ifdef CONFIG_BLK_DEV_INITRD
 static void __init setup_initrd(void)
 {