opcodes: xtensa: display loaded literal value

Display literal value loaded with l32r opcode as a part of disassembly.
This significantly simplifies reading of disassembly output.

2020-04-23  Max Filippov  <jcmvbkbc@gmail.com>
opcodes/
	* xtensa-dis.c (print_xtensa_operand): For PC-relative operand
	of l32r fetch and display referenced literal value.