OvmfPkg: simply use the Bochs interface for vmsvga

BAR  |    std vga     |  vmsvga
---------------------------------
0    |   Framebuffer  | I/O space
1    |   Reserved     | Framebuffer
2    |   MMIO         | FIFO

- We cannot recognize VMW SVGA as BOCHS because that would confuse the
  IsQxl setting in QemuVideoControllerDriverStart(),

- We cannot recognize VMW SVGA as BOCHS_MMIO because BAR2 on VMW SVGA is
  not the BOCHS MMIO BAR (we can only use port IO).

Therefore the list of reasons for which we should introduce
QEMU_VIDEO_VMWARE_SVGA should name three reasons:

 (1) Get framebuffer from correct PCI BAR
 (2) Prevent using BAR2 for MMIO
 (3) Prevent mis-recognizing VMW SVGA as QXL

Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: yuchenlin <yuchenlin@synology.com>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
Regression-tested-by: Laszlo Ersek <lersek@redhat.com>
Tested-by: Laszlo Ersek <lersek@redhat.com>

OvmfPkg/QemuVideoDxe/Driver.c

@@ -69,6 +69,12 @@ QEMU_VIDEO_CARD gQemuVideoCardList[] = {
         0x1050,
         QEMU_VIDEO_BOCHS_MMIO,
         L"QEMU VirtIO VGA"
+    },{
+        PCI_CLASS_DISPLAY_VGA,
+        0x15ad,
+        0x0405,
+        QEMU_VIDEO_VMWARE_SVGA,
+        L"QEMU VMWare SVGA"
     },{
         0 /* end of list */
     }
@@ -316,6 +322,14 @@ QemuVideoControllerDriverStart (
     }
   }
 
+  //
+  // VMWare SVGA is handled like Bochs (with port IO only).
+  //
+  if (Private->Variant == QEMU_VIDEO_VMWARE_SVGA) {
+    Private->Variant = QEMU_VIDEO_BOCHS;
+    Private->FrameBufferVramBarIndex = PCI_BAR_IDX1;
+  }
+
   //
   // Check if accessing the bochs interface works.
   //
@@ -764,7 +778,7 @@ ClearScreen (
   Private->PciIo->Mem.Write (
                         Private->PciIo,
                         EfiPciIoWidthFillUint32,
-                        0,
+                        Private->FrameBufferVramBarIndex,
                         0,
                         0x400000 >> 2,
                         &Color