Save and restore FPU state across suspend and resume.  In earlier revisions
of this patch, resumectx() called npxresume() directly, but that doesn't
work because resumectx() runs with a non-standard %cs selector.  Instead,
all of the FPU suspend/resume handling is done in C.

MFC after:	1 week


git-svn-id: svn+ssh://svn.freebsd.org/base/head@270850 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f