Rewrite (and relicense) the header files which are included in all
builds of iPXE (including non-Linux builds).

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

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

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

Add user access API for linux.

On linux userspace virtual == user == phys addresses.  Physical
addresses also being the same is wrong, but there is no general way of
converting userspace addresses to physical as what appears to be
contiguous in userspace is physically fragmented.  Currently only the
DMA memory is special-cased, but its conversion to bus addresses is
done in phys_to_bus.  This is known to break virtio as it is passing
phys addresses to the virtual device.

Signed-off-by: Piotr Jaroszyński <p.jaroszynski@gmail.com>
Signed-off-by: Michael Brown <mcb30@ipxe.org>