x86-64: more fixes for Fam10 MMCONF enabling

x86-64: more fixes for Fam10 MMCONF enabling

Unfortunately it turned out the original Linux code had more issues:
We want to place the region above 4G in any case (even if TOM2 isn't
enabled or invalid), and the base mask definition was improperly typed
(thus causing shifts by FAM10H_MMIO_CONF_BASE_SHIFT to produce other
than the intended result). Fixing this in turn allowed simplifying the
MMIO region detection code, as regions ending below TOM2 now aren't of
interest anymore.

Signed-off-by: Jan Beulich <jbeulich@novell.com>