hw/arm/raspi: Use RaspiProcessorId to set the firmware load address

The firmware load address depends on the SoC ("processor id") used,
not on the version of the board.

Suggested-by: Luc Michel <luc.michel@greensocs.com>
Reviewed-by: Luc Michel <luc.michel@greensocs.com>
Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-id: 20200924111808.77168-8-f4bug@amsat.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>