MFC 213226:

MFC 213226:
Rewrite the i386 memory probe:
- Check for SMAP data from the loader first.  If it exists, don't bother
  doing any VM86 calls at all.  This will be more friendly for non-BIOS
  boot environments such as EFI, etc.
- Move the base memory setup into a new basemem_setup() routine instead
  of duplicating it.
- Simplify the XEN case by removing all of the VM86/SMAP parsing code rather
  than just jumping over it.
- Adjust some comments to better explain the code flow.

git-svn-id: svn://svn.freebsd.org/base/stable/8@213745 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f