bnxt_en: Add basic XDP support.

Add basic ndo_xdp support to setup and query program, configure the NIC
to run in rx page mode, and support XDP_PASS, XDP_DROP, XDP_ABORTED
actions only.

v3: Pass modified offset and length to stack for XDP_PASS.
    Remove Kconfig option.

v2: Added trace_xdp_exception()
    Added dma_syncs.
    Added XDP headroom support.

Signed-off-by: Michael Chan <michael.chan@broadcom.com>
Tested-by: Andy Gospodarek <gospo@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>