hw/misc: Remove MAINSTONE_FPGA device

The MAINSTONE_FPGA device was used only by the 'mainstone' machine
type, so we can remove it now.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-id: 20240903160751.4100218-12-peter.maydell@linaro.org
3 files changed