hw/hppa/machine: Restrict the total memory size to 3GB

hw/hppa/machine: Restrict the total memory size to 3GB

The hardware expects DIMM slots of 1 or 2 GB, allowing up to
4 GB of memory. We want to accept the same amount of memory the
hardware can deal with. DIMMs of 768MB are not available.

However we have to deal with a firmware limitation: currently
SeaBIOS only supports 32-bit, and expects the RAM size in a
32-bit register. When using a 4GB configuration, the 32-bit
register get truncated and we report a size of 0MB to SeaBIOS,
which ends halting the machine:

  $ qemu-system-hppa -m 4g -serial stdio

  SeaBIOS: Machine configured with too little memory (0 MB), minimum is 16 MB.

  SeaBIOS wants SYSTEM HALT.

The easiest way is to restrict the machine to 3GB of memory.

Acked-by: Helge Deller <deller@gmx.de>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-Id: <20200109000525.24744-3-f4bug@amsat.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>