hw/arm/raspi: Diagnose requests for too much RAM

The Raspberry Pi boards have a physical memory map which does
not allow for more than 1GB of RAM. Currently if the user tries
to ask for more then we fail in a confusing way:

$ qemu-system-aarch64 --machine raspi3 -m 8G
Unexpected error in visit_type_uintN() at qapi/qapi-visit-core.c:164:
qemu-system-aarch64: Parameter 'vcram-base' expects uint32_t
Aborted (core dumped)

Catch this earlier and diagnose it with a more friendly message:
$ qemu-system-aarch64 --machine raspi3 -m 8G
qemu-system-aarch64: Requested ram size is too large for this machine: maximum is 1GB

Fixes: https://bugs.launchpad.net/qemu/+bug/1794187
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Wainer dos Santos Moschetta <wainersm@redhat.com>

hw/arm/raspi.c

@@ -12,6 +12,7 @@
  */
 
 #include "qemu/osdep.h"
+#include "qemu/units.h"
 #include "qapi/error.h"
 #include "qemu-common.h"
 #include "cpu.h"
@@ -175,6 +176,12 @@ static void raspi_init(MachineState *machine, int version)
     BusState *bus;
     DeviceState *carddev;
 
+    if (machine->ram_size > 1 * GiB) {
+        error_report("Requested ram size is too large for this machine: "
+                     "maximum is 1GB");
+        exit(1);
+    }
+
     object_initialize(&s->soc, sizeof(s->soc),
                       version == 3 ? TYPE_BCM2837 : TYPE_BCM2836);
     object_property_add_child(OBJECT(machine), "soc", OBJECT(&s->soc),