hw/riscv: Configurable MPFS CLINT timebase freq

hw/riscv: Configurable MPFS CLINT timebase freq

This property enables the setting of the CLINT timebase frequency
through the command line, for example:

  -machine microchip-icicle-kit,clint-timebase-frequency=10000000

Signed-off-by: Sebastian Huber <sebastian.huber@embedded-brains.de>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-ID: <20250319061342.26435-6-sebastian.huber@embedded-brains.de>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>