NTB: epf: Allow arbitrary BAR mapping

NTB: epf: Allow arbitrary BAR mapping

The NTB epf host driver assumes the BAR number associated with a memory
window is just incremented from the BAR number associated with MW1. This
seems to have been enough so far but this is not really how the endpoint
side work and the two could easily become mis-aligned.

ntb_epf_mw_to_bar() even assumes that the BAR number is the memory window
index + 2, which means the function only returns a proper result if BAR_2
is associated with MW1.

Instead, fully describe and allow arbitrary NTB BAR mapping.

Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>
Signed-off-by: Jon Mason <jdmason@kudzu.us>