resources: ensure callback doesn't allocate outside available space

The alignment callback returns a proposed location, which may have been
adjusted to avoid ISA aliases or for other architecture-specific reasons.

We already had a check ("tmp.start < tmp.end") to make sure the callback
doesn't return an area that extends past the available area.  This patch
reworks the check to make sure it doesn't return an area that extends
either below or above the available area.

Signed-off-by: Bjorn Helgaas <bjorn.helgaas@hp.com>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>