x86: apl: Fix the header order in pmc

The dm.h header should come first. In fact it needs to, since otherwise
the driver model definitions are not available to dt-structs.h

Fix this, since it causes problems with OF_PLATDATA_INST.

Signed-off-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Simon Glass <sjg@chromium.org>