initramfs: Really fix build break on symbol-prefixed archs

Define the __initramfs_size variable using VMLINUX_SYMBOL() to take care
of symbol-prefixed architectures, for example, blackfin.

Signed-off-by: Hendrik Brueckner <[e-mail]>
Cc: Mike Frysinger <[e-mail]>
Cc: Hendrik Brueckner <[e-mail]>,
Cc: Michal Marek <[e-mail]>
Cc: Sam Ravnborg <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
[mmarek: leave out Makefile change, since d63f6d1 already takes care of the
SYMBOL_PREFIX define]
Signed-off-by: Michal Marek <[e-mail]>

usr/initramfs_data.S

···
 */
 
 #include <linux/stringify.h>
+#include <asm-generic/vmlinux.lds.h>
 
 .section .init.ramfs,"a"
 __irf_start:
 .incbin __stringify(INITRAMFS_IMAGE)
 __irf_end:
 .section .init.ramfs.info,"a"
-.globl __initramfs_size
-__initramfs_size:
+.globl VMLINUX_SYMBOL(__initramfs_size)
+VMLINUX_SYMBOL(__initramfs_size):
 #ifdef CONFIG_64BIT
 	.quad __irf_end - __irf_start
 #else