ubsan: xtensa: left shift cannot be represented in type 'int'

ubsan: xtensa: left shift cannot be represented in type 'int'

In Operand_soffsetx4_decode:
  soffsetx4_0 = 0x4 + ((((int) offset_0 << 14) >> 14) << 2);
and other places.

Don't sign extend with shifts!  This file also has many occurrences of
truncation via shifts, which aren't a problem due to using uint32, but
I dislike on principle enough to fix.

	* xtensa-modules.c (Field_* functions): Don't mask using shifts.
	(Operand_soffsetx4_decode, Operand_simm4_decode),
	(Operand_simm8_decode, Operand_simm8x256_decode),
	(Operand_simm12b_decode, Operand_label8_decode),
	(Operand_label12_decode, Operand_soffset_decode),
	(Operand_xt_wbr15_label_decode, Operand_xt_wbr18_label_decode): Don't
	sign extend using shifts.
	(Operand_immrx4_decode, Operand_uimm16x4_decode): Avoid UB in
	constant.