hw/arm/aspeed: Map the UART5 device unconditionally

The UART5 is present on the machine regardless there is a
character device connected to it. Map it unconditionally.

Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Cédric Le Goater <clg@kaod.org>
Message-Id: <20200905212415.760452-1-f4bug@amsat.org>
Signed-off-by: Cédric Le Goater <clg@kaod.org>