[intelxl] Add driver for Intel 100 Gigabit Ethernet NICs

Add a driver for the E810 family of 100 Gigabit Ethernet NICs.  The
core datapath is identical to that of the 40 Gigabit XL710, and this
part of the code is shared between both drivers.  The admin queue
mechanism is sufficiently similar to make it worth reusing substantial
portions of the code, with separate implementations for several
commands to handle the (unnecessarily) breaking changes in data
structure layouts.  The major differences are in the mechanisms for
programming queue contexts (where the E810 abandons TX/RX symmetry)
and for configuring the transmit scheduler and receive filters: these
portions are sufficiently different to justify a separate driver.

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