hw/arm/raspi: Display the board revision in the machine description

hw/arm/raspi: Display the board revision in the machine description

Display the board revision in the machine description.

Before:

  $ qemu-system-aarch64 -M help | fgrep raspi
  raspi2               Raspberry Pi 2B
  raspi3               Raspberry Pi 3B

After:

  raspi2               Raspberry Pi 2B (revision 1.1)
  raspi3               Raspberry Pi 3B (revision 1.2)

Reviewed-by: Luc Michel <luc.michel@greensocs.com>
Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-id: 20200924111808.77168-2-f4bug@amsat.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>