[Differential] D9686: fix UEFI VM's bootup on Hyper-V (i.e. Hyper-V Generation-2 VM)

[decui_microsoft.com (Dexuan Cui)]

decui_microsoft.com added reviewers: tsoome, gonzo, manu, andrew, sbruno, ambrisko, allanjude, bapt, cem, smh, ian.

REVISION DETAIL
  https://reviews.freebsd.org/D9686

EMAIL PREFERENCES
  https://reviews.freebsd.org/settings/panel/emailpreferences/

To: decui_microsoft.com, imp, jhb, will, kib, delphij, emaste, sepherosa_gmail.com, honzhan_microsoft.com, howard0su_gmail.com, marcel, tsoome, gonzo, manu, andrew, sbruno, ambrisko, allanjude, bapt, cem, smh, ian
Cc: freebsd-virtualization-list