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 <ffainelli@freebox.fr>
Acked-by: Grant Likely <grant.likely@secretlab.ca>
Cc: Maxime Bizon <mbizon@freebox.fr>
Acked-by: Sebastian Andrzej Siewior <sebastian@breakpoint.cc>
Cc: stable@kernel.org # 2.6.39
Link: http://lkml.kernel.org/r/201106061015.50039.ffainelli@freebox.frSigned-off-by: Thomas Gleixner <tglx@linutronix.de>

arch/x86/kernel/devicetree.c

@@ -13,6 +13,7 @@
 #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>
@@ -98,6 +99,16 @@ void * __init early_init_dt_alloc_memory_arch(u64 size, u64 align)
 	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)
 {
 	initial_dtb = data + offsetof(struct setup_data, data);