hvmloader/e820: construct guest e820 table

hvmloader/e820: construct guest e820 table

Now use the hypervisor-supplied memory map to build our final e820 table:
* Add regions for BIOS ranges and other special mappings not in the
  hypervisor map
* Add in the hypervisor supplied regions
* Adjust the lowmem and highmem regions if we've had to relocate
  memory (adding a highmem region if necessary)
* Sort all the ranges so that they appear in memory order.

CC: Keir Fraser <keir@xen.org>
CC: Jan Beulich <jbeulich@suse.com>
CC: Andrew Cooper <andrew.cooper3@citrix.com>
CC: Ian Jackson <ian.jackson@eu.citrix.com>
CC: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
CC: Ian Campbell <ian.campbell@citrix.com>
CC: Wei Liu <wei.liu2@citrix.com>
Reviewed-by: George Dunlap <george.dunlap@eu.citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Signed-off-by: Tiejun Chen <tiejun.chen@intel.com>