OvmfPkg: simply use the Bochs interface for vmsvga

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>