net: bootp: add PXE/RFC 4578 DHCP options support

These options are required to be present in RFC 4578 compliant DHCP
requests. They give more information to DHCP servers to allow serving

different DHCP responses to different systems based on client
architecture, client capabilities, UUID, or vendor.

Signed-off-by: Jason Hobbs <jason.hobbs@calxeda.com>