MFV r275535:

Unexpand ISP2() and MSEC2NSEC().

Illumos issue:
    5255 uts shouldn't open-code ISP2

MFC after:	2 weeks


git-svn-id: svn+ssh://svn.freebsd.org/base/head@275562 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f