powerpc: Fix 32-bit SMP boot on CHRP

prom_init was changed to take a new argument, the address
where the kernel is loaded, which is now used to copy the
SMP spin loop down before use.

However, only head_64.S was adapted to pass this new value,
not head_32.S, thus breaking SMP boot on 32-bit SMP CHRP
machines.
Signed-off-by: NBenjamin Herrenschmidt <benh@kernel.crashing.org>

arch/powerpc/kernel/head_32.S

@@ -110,6 +110,12 @@ __start:
 #ifdef CONFIG_PPC_MULTIPLATFORM
 	cmpwi	0,r5,0
 	beq	1f
+
+	/* find out where we are now */
+	bcl	20,31,$+4
+0:	mflr	r8			/* r8 = runtime addr here */
+	addis	r8,r8,(_stext - 0b)@ha
+	addi	r8,r8,(_stext - 0b)@l	/* current runtime base addr */
 	bl	prom_init
 	trap
 #endif