BUILD: add -MMD to iasl cpp call

BUILD: add -MMD to iasl cpp call

Right now there are no dependency rules for compiling dsdt.asl.
If ACPI code includes asl files, the dsdt isn't recompiled if any
of those file is changed. Add the flags to the preprocessor call
to have it generate the neccessary dependency rule.

Signed-off-by: Sven Schnelle <svens@stackframe.org>
Acked-by: Peter Stuge <peter@stuge.se>
git-svn-id: svn://svn.coreboot.org/coreboot/trunk@6456 2b7e53f0-3cfb-0310-b3e9-8179ed1497e1