hw/misc/mips_itu: Declare itc_reconfigure() in 'hw/misc/mips_itu.h'

We already provide "hw/misc/mips_itu.h" to declare prototype
related to MIPSITUState. Move itc_reconfigure() declaration
there.

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20231009171443.12145-3-philmd@linaro.org>