NTB: MFV 53a788a7: Split ntb_setup_interrupts() into SOC, Xeon, and legacy routines

The names don't line up 100% with Linux. Our routines are named
ntb_setup_interrupts, ntb_setup_xeon_msix, ntb_setup_soc_msix, and
ntb_setup_legacy_interrupt. Linux SNB = FreeBSD Xeon; Linux BWD =
FreeBSD SOC. Original Linux commit log:

This is an cleanup effort to make ntb_setup_msix() more readable - use
ntb_setup_bwd_msix() to init MSI-Xs on BWD hardware and
ntb_setup_snb_msix() - on SNB hardware.

Function ntb_setup_snb_msix() also initializes MSI-Xs the way it should
has been done - looping pci_enable_msix() until success or failure.

Authored by: Alexander Gordeev
Obtained from: Linux (Dual BSD/GPL driver)
Sponsored by: EMC / Isilon Storage Division