cxgb4vf: remove obsolete DECLARE_PCI_UNMAP_ADDR usage

We could use DEFINE_DMA_UNMAP_ADDR instead but using
CONFIG_NEED_DMA_MAP_STATE is a simpler way to see if a platform does
real DMA unmapping.

Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Signed-off-by: David S. Miller <davem@davemloft.net>