MFC 221138:

MFC 221138:
Only align MSI message groups based on the number of messages being
allocated, not the maximum number of messages the device supports.  The
spec only requires the former, and I believe I implemented the latter due
to misunderstanding an e-mail.  In particular, this fixes an issue where
having several devices that all support 16 messages can run out of
IDT vectors on x86 even though the driver only uses a single message.

git-svn-id: svn://svn.freebsd.org/base/stable/8@222837 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f