c4x.c (legitimize_operands): Use rtx_cost to determine if it is worthwhile forcing a constant into a register.

	* config/c4x/c4x.c (legitimize_operands): Use rtx_cost
	to determine if it is worthwhile forcing a constant into a register.
	* config/c4x/c4x.h (CONST_COSTS): An integer value of 255 or 65535
	used with a logical and or an integer value of 16 or 24 used with
	a right shift has zero cost on the C40.

From-SVN: r26529