mlx5, xsk: Migrate to new MEM_TYPE_XSK_BUFF_POOL

Use the new MEM_TYPE_XSK_BUFF_POOL API in lieu of MEM_TYPE_ZERO_COPY in
mlx5e. It allows to drop a lot of code from the driver (which is now
common in AF_XDP core and was related to XSK RX frame allocation, DMA
mapping, etc.) and slightly improve performance (RX +0.8 Mpps, TX +0.4
Mpps).

rfc->v1: Put back the sanity check for XSK params, use XSK API to get
         the total headroom size. (Maxim)

v1->v2: Fix DMA address handling, set XDP metadata to invalid. (Maxim)

v2->v3: Handle frame_sz, use xsk_buff_xdp_get_frame_dma, use xsk_buff
        API for DMA sync on TX, add performance numbers. (Maxim)

v3->v4: Remove unused variable num_xsk_frames. (Jakub)

Signed-off-by: Björn Töpel <bjorn.topel@intel.com>
Signed-off-by: Maxim Mikityanskiy <maximmi@mellanox.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20200520192103.355233-12-bjorn.topel@gmail.com