target-arm: Implement BCM2835 hardware RNG

Recent vanilla Raspberry Pi kernels started to make use of
the hardware random number generator in BCM2835 SoC. As a
result, those kernels wouldn't work anymore under QEMU
but rather just freeze during the boot process.

This patch implements a trivial BCM2835 compatible RNG,
and adds it as a peripheral to BCM2835 platform, which
allows to boot a vanilla Raspberry Pi kernel under Qemu.

Changes since v1:
 * Prevented guest from writing [31..20] bits in rng_status
 * Removed redundant minimum_version_id_old
 * Added field entries for the state
 * Changed realize function to reset

Signed-off-by: Marcin Chojnacki <marcinch7@gmail.com>
Message-id: 20170210210857.47893-1-marcinch7@gmail.com
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

include/hw/arm/bcm2835_peripherals.h

@@ -19,6 +19,7 @@
 #include "hw/dma/bcm2835_dma.h"
 #include "hw/intc/bcm2835_ic.h"
 #include "hw/misc/bcm2835_property.h"
+#include "hw/misc/bcm2835_rng.h"
 #include "hw/misc/bcm2835_mbox.h"
 #include "hw/sd/sdhci.h"
 
@@ -41,6 +42,7 @@ typedef struct BCM2835PeripheralState {
     BCM2835DMAState dma;
     BCM2835ICState ic;
     BCM2835PropertyState property;
+    BCM2835RngState rng;
     BCM2835MboxState mboxes;
     SDHCIState sdhci;
 } BCM2835PeripheralState;