x86: devicetree: Add missing early_init_dt_setup_initrd_arch stub

This patch fixes the following build failure:

drivers/built-in.o: In function `early_init_dt_check_for_initrd':
/home/florian/dev/kernel/x86/linux-2.6-x86/drivers/of/fdt.c:571:
undefined reference to `early_init_dt_setup_initrd_arch'
make: *** [.tmp_vmlinux1] Error 1

which happens as soon as we enable initrd support on a x86 devicetree
platform such as Intel CE4100.

Signed-off-by: Florian Fainelli <[e-mail]>
Acked-by: Grant Likely <[e-mail]>
Cc: Maxime Bizon <[e-mail]>
Acked-by: Sebastian Andrzej Siewior <[e-mail]>
Cc: [e-mail] # 2.6.39
Link: http://lkml.kernel.org/r/[e-mail]
Signed-off-by: Thomas Gleixner <[e-mail]>

arch/x86/kernel/devicetree.c

···
 #include <linux/slab.h>
 #include <linux/pci.h>
 #include <linux/of_pci.h>
+#include <linux/initrd.h>
 
 #include <asm/hpet.h>
 #include <asm/irq_controller.h>
···
 {
 	return __alloc_bootmem(size, align, __pa(MAX_DMA_ADDRESS));
 }
+
+#ifdef CONFIG_BLK_DEV_INITRD
+void __init early_init_dt_setup_initrd_arch(unsigned long start,
+					    unsigned long end)
+{
+	initrd_start = (unsigned long)__va(start);
+	initrd_end = (unsigned long)__va(end);
+	initrd_below_start_ok = 1;
+}
+#endif
 
 void __init add_dtb(u64 data)
 {