libxc: Prepare a start info structure for hvmloader

libxc: Prepare a start info structure for hvmloader

... and load BIOS/UEFI firmware into guest memory.

This adds a new firmware module, system_firmware_module. It is loaded in
the guest memory and final location is provided to hvmloader via the
hvm_start_info struct.

This patch create the hvm_start_info struct for HVM guest that have a
device model, so this is now common code with HVM guest without device
model.

Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>
Acked-by: Wei Liu <wei.liu2@citrix.com>