powerpc/32: Add .data.rel* sections explicitly

Match powerpc/64 and include .data.rel* input sections in the .data output
section explicitly.

This solves the warning:

powerpc-linux-gnu-ld: warning: orphan section `.data.rel.ro' from `arch/powerpc/kernel/head_44x.o' being placed in section `.data.rel.ro'.

Link: https://lists.01.org/pipermail/kbuild-all/2017-November/040010.html
Reported-by: kbuild test robot <fengguang.wu@intel.com>
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/kernel/vmlinux.lds.S

@@ -264,6 +264,7 @@ SECTIONS
 #ifdef CONFIG_PPC32
 	.data : AT(ADDR(.data) - LOAD_OFFSET) {
 		DATA_DATA
+		*(.data.rel*)
 		*(.sdata)
 		*(.sdata2)
 		*(.got.plt) *(.got)