OvmfPkg: Install BGRT ACPI table

OvmfPkg: Install BGRT ACPI table

While debugging OS for ACPI BGRT support (especially on VMs),
it is very useful to have the EFI firmware (OVMF in most cases
which use Tianocore) to export the ACPI BGRT table.

This patch tries to add this support in OvmfPkg.

Tested this patch in the following environments:

1. On both RHEL7.3 and Fedora-25 VM guests running on a Fedora-24 Host:
   - Ensured that the BGRT logo is properly prepared and
     can be viewed with user-space tools (like 'Gwenview' on KDE,
     for example):

     $ file /sys/firmware/acpi/bgrt/image
     /sys/firmware/acpi/bgrt/image: PC bitmap, Windows 3.x format, 193 x
     58 x 24

2. On a Windows-10 VM Guest running on a Fedora-24 Host:
   - Ensured that the BGRT ACPI table is properly prepared and can be
     read with freeware tool like FirmwareTablesView:

     ==================================================
     Signature         : BGRT
     Firmware Provider : ACPI
     Length            : 56
     Revision          : 1
     Checksum          : 129
     OEM ID            : INTEL
     OEM Table ID      : EDK2
     OEM Revision      : 0x00000002
     Creator ID        : 0x20202020
     Creator Revision  : 0x01000013
     Description       :
     ==================================================

Note from Laszlo Ersek <lersek@redhat.com>: without the BGRT ACPI table,
Windows 8 and Windows 10 first clear the screen, then display a blue,
slanted Windows picture above the rotating white boot animation. With the
BGRT ACPI table, Windows 8 and Windows 10 don't clear the screen, the blue
Windows image is not displayed, and the rotating white boot animation is
shown between the firmware's original TianoCore boot splash and (optional)
"Start boot option" progress bar.

Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Laszlo Ersek <lersek@redhat.com>
Signed-off-by: Bhupesh Sharma <bhsharma@redhat.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
Tested-by: Laszlo Ersek <lersek@redhat.com>
[lersek@redhat.com: cover effect on Windows 8/10 boot anim. in commit msg]
Signed-off-by: Laszlo Ersek <lersek@redhat.com>