acpi: Move MCFG implementation to common lib

MCFG tables are used on multiple arches. Move to common ACPI lib.

Cc: Simon Glass <sjg@chromium.org>
Signed-off-by: Moritz Fischer <moritzf@google.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Use sizeof(*mcfg) instead of sizeof(*header)
Signed-off-by: Simon Glass <sjg@chromium.org>