Enlarge i386/x86-64 kernel command line to 2k

This is useful when the kernel command line is used to pass other
information to initrds or installers.

On i386 it was duplicated for unknown reasons.
Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>