MFC 310048,310101

MFC 310048,310101

310048
    hyperv: Implement "enlightened" time counter, which is rdtsc based.

    Reviewed by:    kib
    Sponsored by:   Microsoft
    Differential Revision:  https://reviews.freebsd.org/D8763

310101
    hyperv: Allow userland to ro-mmap reference TSC page

    This paves way to implement VDSO for the enlightened time counter.

    Reviewed by:    kib
    Sponsored by:   Microsoft
    Differential Revision:  https://reviews.freebsd.org/D8768

git-svn-id: svn://svn.freebsd.org/base/stable/10@311223 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f