memory: fix rendering of a region obscured by another

memory: fix rendering of a region obscured by another

The memory core drops regions that are hidden by another region (for example,
during BAR sizing), but it doesn't do so correctly if the lower address of the
existing range is below the lower address of the new range.

Example (qemu-system-mips -M malta -kernel vmlinux-2.6.32-5-4kc-malta
         -append "console=ttyS0"  -nographic -vga cirrus):

Existing range: 10000000-107fffff
New range:      100a0000-100bffff

Correct behaviour: drop new range
Incorrect behaviour: add new range

Fix by taking this case into account (previously we only considered
equal lower boundaries).

Tested-by: Aurelien Jarno <aurelien@aurel32.net>
Signed-off-by: Avi Kivity <avi@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>