OvmfPkg/QemuBootOrderLib: drop too strict "/HD(" suffix from vblk prefix

OvmfPkg/QemuBootOrderLib: drop too strict "/HD(" suffix from vblk prefix

Translating QEMU's virtio-block OpenFirmware device path to a UEFI device
path prefix was one of the earliest case handled in QemuBootOrderLib. At
that time, I terminated the translation output (the UEFI devpath prefix)
with a "/HD(" suffix.

The intent was for the translation to prefix-match only boot options with
HD() device path nodes in them, that is, no auto-generated "device level"
boot options. This was motivated by prioritizing specific boot options
created by OS installers over auto-generated "device level" options.

However, practice has shown that:

- OS installers place their installed boot options first in the boot order
  anyway,

- other device types (SATA disks, virtio-scsi disks), where "/HD(" is not
  appended, work just fine,

- requiring "/HD(" actually causes problems: after the OS-installed
  specific boot option has been lost (or purposely removed), the
  auto-generated "device level" boot option does the right thing (see the
  Default Boot Behavior under
  <http://blog.uncooperative.org/blog/2014/02/06/the-efi-system-partition/>).
  The "/HD(" requirement causes such boot options to be dropped, which
  prevents "fallback.efi" from running.

Relax the matching by removing the "/HD(" suffix from the translated
prefix.

Cc: Jordan Justen <jordan.l.justen@intel.com>
Fixes: e06a4cd134064590aa1a855ff4b973023279e805
Ref: https://bugzilla.redhat.com/show_bug.cgi?id=1373812
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>