OvmfPkg/PlatformBootManagerLib: bring back the progress bar

OVMF's Platform BDS used to have a nice progress bar (with
IntelFrameworkModulePkg BDS). We can restore it by copying the
PlatformBootManagerWaitCallback() function verbatim from

  Nt32Pkg/Library/PlatformBootManagerLib/PlatformBootManager.c

It can be tested by passing the following option to QEMU (5 seconds):

  -boot menu=on,splash-time=5000

Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Ruiyu Ni <ruiyu.ni@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>

OvmfPkg/Library/PlatformBootManagerLib/BdsPlatform.c

@@ -1425,5 +1425,22 @@ PlatformBootManagerWaitCallback (
   UINT16          TimeoutRemain
   )
 {
+  EFI_GRAPHICS_OUTPUT_BLT_PIXEL_UNION Black;
+  EFI_GRAPHICS_OUTPUT_BLT_PIXEL_UNION White;
+  UINT16                              Timeout;
+
+  Timeout = PcdGet16 (PcdPlatformBootTimeOut);
+
+  Black.Raw = 0x00000000;
+  White.Raw = 0x00FFFFFF;
+
+  BootLogoUpdateProgress (
+    White.Pixel,
+    Black.Pixel,
+    L"Start boot option",
+    White.Pixel,
+    (Timeout - TimeoutRemain) * 100 / Timeout,
+    0
+    );
 }