ArmPkg/PlatformBootManagerLib: print firmware version to console

ArmPkg/PlatformBootManagerLib: print firmware version to console

If gEfiMdeModulePkgTokenSpaceGuid.PcdFirmwareVersionString is set to
a non-empty string, print it to the console at boot. Note that this
is independent of DEBUG/RELEASE or graphical vs serial console,
although we do attempt to stay clear of the logo and progress bar
in graphical mode, by printing it top center.

Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>