ArmVirtPkg/ArmVirtKvmTool: wire up configurable timeout

ArmVirtPkg/ArmVirtKvmTool: wire up configurable timeout

Use the correct PCD type for PcdPlatformBootTimeOut so it gets wired up
to the Timeout EFI variable automatically, which is how the boot manager
stores the timeout preference.

Note that this changes the default to 5 seconds, which appears to be
common across platforms.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Reviewed-by: Pierre Gondois <pierre.gondois@arm.com>
Reviewed-by: Sami Mujawar <sami.mujawar@arm.com>