[PATCH] Include <linux/config.h> before testing CONFIG_ACPI

I'm not sure why this issue is suddenly showing, but without this
patchlet, the zx1 config won't compile anymore (e.g., to see the
compilation-error, look for "***" in [1]).

[1] http://www.gelato.unsw.edu.au/kerncomp/results//2005-06-06-17-00/zx1_defconfig-log.html

Signed-off-by: David Mosberger-Tang <davidm@hpl.hp.com>
Cc: "Brown, Len" <len.brown@intel.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>