dmi: clean-up dmi helper declarations

The declaration of dmi helper functions is a bit messy and inconsistent at the
moment:

* On ia64 they are declared in <asm/io.h>.
* On x86-64 they are declared in <asm/dmi.h>.
* On i386 they are declared both in <asm/io.h> and <asm/dmi.h>.

Fix the header files so that the dmi helper functions are consistently
defined in <asm/dmi.h>.

Signed-off-by: Jean Delvare <khali@linux-fr.org>
Cc: Matt Domsch <Matt_Domsch@dell.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>