net: qcom/emac: Use proper free methods during TX

This patch fixes the warning messages/call traces seen if DMA debug is
enabled, In case of fragmented skb's memory was allocated using
dma_map_page but freed using dma_unmap_single. This patch modifies buffer
allocations in TX path to use dma_map_page in all the places and
dma_unmap_page while freeing the buffers.

Signed-off-by: Hemanth Puranik <hpuranik@codeaurora.org>
Acked-by: Timur Tabi <timur@codeaurora.org>
Signed-off-by: David S. Miller <davem@davemloft.net>