This patch adds the support for receiving packet via AF_XDP zero-copy
mechanism.

XDP ZC uses 1:1 mapping of XDP buffer to receive packet, therefore the
use of split header is not used currently. The 'xdp_buff' is declared as
union together with a struct that contains 'page', 'addr' and
'page_offset' that are associated with primary buffer.

RX buffers are now allocated either via page_pool or xsk pool. For RX
buffers from xsk_pool they are allocated and deallocated using below
functions:

 * stmmac_alloc_rx_buffers_zc(struct stmmac_priv *priv, u32 queue)
 * dma_free_rx_xskbufs(struct stmmac_priv *priv, u32 queue)

With above functions now available, we then extend the following driver
functions to support XDP ZC:
 * stmmac_reinit_rx_buffers()
 * __init_dma_rx_desc_rings()
 * init_dma_rx_desc_rings()
 * __free_dma_rx_desc_resources()

Note: stmmac_alloc_rx_buffers_zc() may return -ENOMEM due to RX XDP
buffer pool is not allocated (e.g. samples/bpf/xdpsock TX-only). But,
it is still ok to let TX XDP ZC to continue, therefore, the -ENOMEM
is silently ignored to let the driver succcessfully transition to XDP
ZC mode for the said RX and TX queue.

As XDP ZC buffer size is different, the DMA buffer size is required
to be reprogrammed accordingly for RX DMA/Queue that is populated with
XDP buffer from XSK pool.

Next, to add or remove per-queue XSK pool, stmmac_xdp_setup_pool()
will call stmmac_xdp_enable_pool() or stmmac_xdp_disable_pool()
that in-turn coordinates the tearing down and setting up RX ring via
RX buffers and descriptors removal and reallocation through
stmmac_disable_rx_queue() and stmmac_enable_rx_queue(). In addition,
stmmac_xsk_wakeup() is added to initiate XDP RX buffer replenishing
by signalling user application to add available XDP frames back to
FILL queue.

For RX processing using XDP zero-copy buffer, stmmac_rx_zc() is
introduced which is implemented with the assumption that RX split
header is disabled. For XDP verdict is XDP_PASS, the XDP buffer is
copied into a sk_buff allocated through stmmac_construct_skb_zc()
and sent to Linux network GRO inside stmmac_dispatch_skb_zc(). Free RX
buffers are then replenished using stmmac_rx_refill_zc()

v2: introduce __stmmac_disable_all_queues() to contain the original code
    that does napi_disable() and then make stmmac_setup_tc_block_cb()
    to use it. Move synchronize_rcu() into stmmac_disable_all_queues()
    that eventually calls __stmmac_disable_all_queues(). Then,
    make both stmmac_release() and stmmac_suspend() to use
    stmmac_disable_all_queues(). Thanks David Miller for spotting the
    synchronize_rcu() issue in v1 patch.
Signed-off-by: Ong Boon Leong <boon.leong.ong@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>