Drop support for ACPI 3 E820 extended memory attributes

Drop support for ACPI 3 E820 extended memory attributes

Drop all support for ACPI 3 E820 extended memory attributes.  There
are BIOSes in the field that report completely bogus information here,
resulting in no memory at all being detected (we then fall back to
E801 detection, but that is problematic in its own ways.)

There is strong reasons to believe at this point that the extended
memory attributes are not usable in their current form, so drop them
and revert back to simple 20-byte support, including for MEMDISK
spoofing.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>