kexec: extend hypercall for efi memory map, boot parameter and xenheap regions

kexec: extend hypercall for efi memory map, boot parameter and xenheap regions

Extend the kexec hypercall to allow it to return the efi memory map,
boot parameter and xen heap regions.

The efi memory map and boot parameter regions need to be supplied
by xen to dom0, rather than established by dom0 as dom0's memory
is not machine memory and thus the regions are not in the correct
location. These regions are inserted into machine_iomem by dom0.

The xen heap region is needed as on xen the hypervisor code and
heap exist in two different EFI memory regions, which are
reflected in machine_iomem. Thus a single xen code region can't be
inserted into machine_iomem.

Signed-off-by: Simon Horman <horms@verge.net.au>