gas: xtensa: reuse trampoline placement code

gas: xtensa: reuse trampoline placement code

There's almost exact copy of the trampoline placement code in the
search_trampolines function that is used for jumps generated for relaxed
branch instructions. Get rid of the duplication and reuse
xg_find_best_trampoline function for that.

gas/
2017-11-27  Max Filippov  <jcmvbkbc@gmail.com>

	* config/tc-xtensa.c (search_trampolines, get_best_trampoline):
	Remove definitions.
	(xg_find_best_trampoline_for_tinsn): New function.
	(relax_frag_immed): Replace call to get_best_trampoline with a
	call to xg_find_best_trampoline_for_tinsn.
	* testsuite/gas/xtensa/trampoline.d: Adjust absolute addresses
	as the placement of trampolines for relaxed branches has been
	changed.