x86: devicetree: Add missing early_init_dt_setup_initrd_arch stub

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