ArmVirtPkg/PlatformBootManagerLib: connect Virtio RNG devices again

ArmVirtPkg/PlatformBootManagerLib: connect Virtio RNG devices again

Virtio RNG devices are never boot devices, so in commit ff1d0fbfbaec we
stopped connecting them. This is a problem because an OS boot loader may
depend on EFI_RNG_PROTOCOL to seed the OS's RNG.

Connect Virtio RNG devices again. And, while commit ff1d0fbfbaec removed
that from PlatformBootManagerAfterConsole(), reintroduce it now to
PlatformBootManagerBeforeConsole() -- this way Driver#### options launched
between both functions may access EFI_RNG_PROTOCOL too.

Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Fixes: ff1d0fbfbaec55038ccf888759588fa4e21516f4
Ref: https://bugzilla.redhat.com/show_bug.cgi?id=1579518
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>