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/Qemu.h

@@ -92,6 +92,7 @@ typedef enum {
   QEMU_VIDEO_CIRRUS_5446,
   QEMU_VIDEO_BOCHS,
   QEMU_VIDEO_BOCHS_MMIO,
+  QEMU_VIDEO_VMWARE_SVGA,
 } QEMU_VIDEO_VARIANT;
 
 typedef struct {
@@ -120,6 +121,7 @@ typedef struct {
   QEMU_VIDEO_VARIANT                    Variant;
   FRAME_BUFFER_CONFIGURE                *FrameBufferBltConfigure;
   UINTN                                 FrameBufferBltConfigureSize;
+  UINT8                                 FrameBufferVramBarIndex;
 } QEMU_VIDEO_PRIVATE_DATA;
 
 ///