xtensa: gas: clean up literal management code

xtensa: gas: clean up literal management code

gas/
2019-04-11  Max Filippov  <jcmvbkbc@gmail.com>

	* config/tc-xtensa.c (xtensa_literal_pseudo): Drop code that has
	no effect.
	(get_literal_pool_location): Only search for the literal pool
	when auto litpools is used, otherwise take one recorded in the
	tc_segment_info_data.
	(xtensa_assign_litpool_addresses): New function.
	(xtensa_move_literals): Don't duplicate 'literal pool location
	required...' error message. Call xtensa_assign_litpool_addresses.