ArmVirtPkg/PlatformBootManagerLib: sync Timeout with PcdPlatformBootTimeOut

ArmVirtPkg/PlatformBootManagerLib: sync Timeout with PcdPlatformBootTimeOut

Set the Timeout global variable to the same value as
PcdPlatformBootTimeOut. This way the "setvar" command in the UEFI shell,
and the "efibootmgr" command in a Linux guest, can report the front page
timeout that was requested on the QEMU command line (see
GetFrontPageTimeoutFromQemu()).

A DEBUG_VERBOSE message is logged on success too, for our QE team's sake.

Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Leif Lindholm <leif@nuviainc.com>
Cc: Philippe Mathieu-Daudé <philmd@redhat.com>
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Message-Id: <20200304094413.19462-3-lersek@redhat.com>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Philippe Mathieu-Daude <philmd@redhat.com>