PCI/x86: document pci=earlydump argument

Document the "pci=earlydump" argument.  This currently only works on x86.
Signed-off-by: NBjorn Helgaas <bjorn.helgaas@hp.com>
Signed-off-by: NJesse Barnes <jbarnes@virtuousgeek.org>

Documentation/kernel-parameters.txt

@@ -1659,6 +1659,8 @@ and is between 256 and 4096 characters. It is defined in the file
 			See also Documentation/blockdev/paride.txt.
 
 	pci=option[,option...]	[PCI] various PCI subsystem options:
+		earlydump	[X86] dump PCI config space before the kernel
+			        changes anything
 		off		[X86] don't probe for the PCI bus
 		bios		[X86-32] force use of PCI BIOS, don't access
 				the hardware directly. Use this if your machine