OvmfPkg: PlatformBdsLib: get front page timeout from QEMU

OvmfPkg: PlatformBdsLib: get front page timeout from QEMU

Put QemuBootOrderLib's GetFrontPageTimeoutFromQemu() to use, so that
OVMF's Platform BDS policy can consume QEMU's command line option

  -boot menu=on,splash-time=N

RHBZ: https://bugzilla.redhat.com/show_bug.cgi?id=1170507

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@16611 6f19259b-4bc3-4df7-8a09-765794883524