[efi] Use load memory address as file offset for hybrid binaries

[efi] Use load memory address as file offset for hybrid binaries

Hybrid bzImage and UEFI binaries (such as wimboot) may be loaded as a
single contiguous blob without reference to the PE headers, and the
placement of sections within the PE file must therefore be known at
link time.

Use the load memory address (extracted from the ELF program headers)
to determine the physical placement of the section within the PE file
when generating a hybrid binary.

Signed-off-by: Michael Brown <mcb30@ipxe.org>