QemuOpenBoardPkg: Enable stage 3

This patch adds MinPlatform stage 3 (UEFI boot) functionality
Stage 3 adds DxeMain, drivers and modules necessary to reach UEFI shell.

Cc: Leif Lindholm <quic_llindhol@quicinc.com>
Cc: Michael D Kinney <michael.d.kinney@intel.com>
Cc: Isaac Oram <isaac.w.oram@intel.com>
Cc: Pedro Falcato <pedro.falcato@gmail.com>
Cc: Gerd Hoffmann <kraxel@redhat.com>
Cc: Stefan Hajnoczi <stefanha@gmail.com>
Signed-off-by: Theo Jehl <theojehl76@gmail.com>
Series Reviewed-by: Isaac Oram <isaac.w.oram@intel.com>
Acked-by: Michael D Kinney <michael.d.kinney@intel.com>
Series-Reviewed-by: Pedro Falcato <pedro.falcato@gmail.com>