hw/arm/raspi: Add the Raspberry Pi A+ machine

hw/arm/raspi: Add the Raspberry Pi A+ machine

The Pi A is almost the first machine released.
It uses a BCM2835 SoC which includes a ARMv6Z core.

Example booting the machine using content from [*]
(we use the device tree from the B model):

  $ qemu-system-arm -M raspi1ap -serial stdio \
      -kernel raspberrypi/firmware/boot/kernel.img \
      -dtb raspberrypi/firmware/boot/bcm2708-rpi-b-plus.dtb \
      -append 'earlycon=pl011,0x20201000 console=ttyAMA0'
  [    0.000000] Booting Linux on physical CPU 0x0
  [    0.000000] Linux version 4.19.118+ (dom@buildbot) (gcc version 4.9.3 (crosstool-NG crosstool-ng-1.22.0-88-g8460611)) #1311 Mon Apr 27 14:16:15 BST 2020
  [    0.000000] CPU: ARMv6-compatible processor [410fb767] revision 7 (ARMv7), cr=00c5387d
  [    0.000000] CPU: VIPT aliasing data cache, unknown instruction cache
  [    0.000000] OF: fdt: Machine model: Raspberry Pi Model B+
  ...

[*] http://archive.raspberrypi.org/debian/pool/main/r/raspberrypi-firmware/raspberrypi-kernel_1.20200512-2_armhf.deb

Reviewed-by: Igor Mammedov <imammedo@redhat.com>
Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-id: 20201024170127.3592182-8-f4bug@amsat.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>