MFC: r343578 (partial)

• Stop iflib(4) from leaking MSI messages on detachment by calling bus_teardown_intr(9) before pci_release_msi(9).
• Ensure that iflib(4) and associated drivers pass correct RIDs to bus_release_resource(9) by obtaining the RIDs via rman_get_rid(9) on the corresponding resources instead of using the RIDs initially passed to bus_alloc_resource_any(9) as the latter function may change those RIDs. Solely em(4) for the ioport resource (but not others) and bnxt(4) were using the correct RIDs by caching the ones returned by bus_alloc_resource_any(9).
• Change the logic of iflib_msix_init() around to only map the MSI-X BAR if MSI-X is actually supported, i. e. pci_msix_count(9) returns > 0. Otherwise the "Unable to map MSIX table " message triggers for devices that simply don't support MSI-X and the user may think that something is wrong while in fact everything works as expected.
• Put some (mostly redundant) debug messages emitted by iflib(4) and em(4) during attachment under bootverbose. The non-verbose output of em(4) seen during attachment now is close to the one prior to the conversion to iflib(4).
• Replace various variants of spelling "MSI-X" (several in messages) with "MSI-X" as used in the PCI specifications.
• Remove some trailing whitespace from messages emitted by iflib(4) and change them to consistently start with uppercase.
• Remove some obsolete comments about releasing interrupts from drivers and correct a few others.

Reviewed by: erj, Jacob Keller, shurd
Differential Revision: https://reviews.freebsd.org/D18980