net: ethernet: xilinx: Mark XILINX_LL_TEMAC broken on 64-bit

On 64-bit (e.g. powerpc64/allmodconfig):

    drivers/net/ethernet/xilinx/ll_temac_main.c: In function 'temac_start_xmit_done':
    drivers/net/ethernet/xilinx/ll_temac_main.c:633:22: warning: cast to pointer from integer of different size [-Wint-to-pointer-cast]
	dev_kfree_skb_irq((struct sk_buff *)cur_p->app4);
			  ^

cdmac_bd.app4 is u32, so it is too small to hold a kernel pointer.

Note that several other fields in struct cdmac_bd are also too small to
hold physical addresses on 64-bit platforms.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: David S. Miller <davem@davemloft.net>