m32r sim: Add prototypes for functions that pass/return DI values

	* m32r-sim.h (m32rbf_h_accum_get_handler): Always provide a
	prototype for this function.
	(m32rbf_h_accum_set_handler): Likewise.
	(m32r2f_h_accums_get_handler): Prototype.
	(m32r2f_h_accums_set_handler): Prototype.