Allow optionroms and "low mem" to share space.

Allow optionroms and "low mem" to share space.

Allow both optionroms and "low mem" allocations to use the e-segment.
(Space is allocated on a "first come, first serve" basis).  This
allows more flexibility in resource assignment.

Also, allow the "low mem" area to use a full 64K.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>