MFC 297932,298295:

MFC 297932,298295:
Improvements for PCI passthru devices.

297932:
Handle PBA that shares a page with MSI-X table for passthrough devices.

If the PBA shares a page with the MSI-X table, map the shared page via
/dev/mem and emulate accesses to the portion of the PBA in the shared
page by accessing the mapped page.

298295:
Always emit an error message on passthru configuration errors.

Previously, many errors (such as the PCI device not being attached
to the ppt(4) driver) resulted in bhyve silently exiting without
starting the virtual machine.  Now any errors encountered when
configuring a virtual slot for a PCI passthru device should be noted
on stderr.

git-svn-id: svn://svn.freebsd.org/base/stable/10@298724 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f