drm/nouveau: enable the ttm dma pool when swiotlb is active V3

If the card is capable of more than 32-bit, then use the default
TTM page pool code which allocates from anywhere in the memory.

Note: If the 'ttm.no_dma' parameter is set, the override is ignored
and the default TTM pool is used.

V2 use pci_set_consistent_dma_mask
V3 Rebase on top of no memory account changes (where/when is my
   delorean when i need it ?)

CC: Ben Skeggs <bskeggs@redhat.com>
CC: Francisco Jerez <currojerez@riseup.net>
CC: Dave Airlie <airlied@redhat.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Reviewed-by: Jerome Glisse <jglisse@redhat.com>