[int13] Add infrastructure to support EDD version 4.0

[int13] Add infrastructure to support EDD version 4.0

Support the extensions mandated by EDD 4.0, including:

 o  the ability to specify a flat physical address in a disk address
    packet,

 o  the ability to specify a sector count greater than 127 in a disk
    address packet,

 o  support for all functions within the Fixed Disk Access and EDD
    Support subsets,

 o  the ability to describe a device using EDD Device Path Information.

This implementation is based on draft revision 3 of the EDD 4.0
specification, with reference to the EDD 3.0 specification.  It is
possible that this implementation may need to change in order to
conform to the final published EDD 4.0 specification.

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