ArmVirtPkg/PlatformBootManagerLib: add EnableQuietBoot & DisableQuietBoot

UefiBootManagerLib does not provide these functions, we have to implement
them. (EnableQuietBoot() puts up the nice TianoCore logo.)

OvmfPkg commits 817fb3ac2a and 8e8fd30377 have extracted these
functions already,
- from "IntelFrameworkModulePkg/Library/GenericBdsLib/BdsConsole.c"
- to "OvmfPkg/Library/PlatformBootManagerLib/QuietBoot.c".

Copy the latter file, with minimal changes.

Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Ruiyu Ni <ruiyu.ni@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Tested-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Ruiyu Ni <ruiyu.ni@Intel.com>

ArmVirtPkg/Library/PlatformBootManagerLib/PlatformBm.h

@@ -48,4 +48,33 @@ TryRunningQemuKernel (
   VOID
   );
 
+/**
+  Use SystemTable Conout to stop video based Simple Text Out consoles from
+  going to the video device. Put up LogoFile on every video device that is a
+  console.
+
+  @param[in]  LogoFile   File name of logo to display on the center of the
+                         screen.
+
+  @retval EFI_SUCCESS     ConsoleControl has been flipped to graphics and logo
+                          displayed.
+  @retval EFI_UNSUPPORTED Logo not found
+**/
+EFI_STATUS
+EnableQuietBoot (
+  IN  EFI_GUID  *LogoFile
+  );
+
+/**
+  Use SystemTable Conout to turn on video based Simple Text Out consoles. The
+  Simple Text Out screens will now be synced up with all non video output
+  devices
+
+  @retval EFI_SUCCESS     UGA devices are back in text mode and synced up.
+**/
+EFI_STATUS
+DisableQuietBoot (
+  VOID
+  );
+
 #endif // _PLATFORM_BM_H_