x86: undo visws/numaq build changes

arch/x86/pci/Makefile_32 has a nasty detail. VISWS and NUMAQ build
override the generic pci-y rules. This needs a proper cleanup, but
that needs more thoughts. Undo

commit 895d3093
    x86: numaq fix
    do not override the existing pci-y rule when adding visws or
    numaq rules.

There is also a stupid init function ordering problem vs. acpi.o

Add comments to the Makefile to avoid tripping over this again.

Remove the srat stub code in discontig_32.c to allow a proper NUMAQ
build.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>