ACPI: Reorder IPMI driver before any other ACPI drivers

Drivers may make calls that require the ACPI IPMI driver to have been
initialised already, so make sure that it appears earlier in the build
order.

Signed-off-by: Matthew Garrett <mjg@redhat.com>
Signed-off-by: Corey Minyard <cminyard@mvista.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>