xtensa: ld: convert tests to run_dump_test

xtensa: ld: convert tests to run_dump_test

Three tests with individual .exp files can be implemented in less
verbose way with run_dump_test infrastructure. Convert them.

ld/
2018-07-23  Max Filippov  <jcmvbkbc@gmail.com>

	* testsuite/ld-xtensa/coalesce.d: New file.
	* testsuite/ld-xtensa/coalesce.exp: Remove file.
	* testsuite/ld-xtensa/diff_overflow.d: New file.
	* testsuite/ld-xtensa/diff_overflow.exp: Remove file.
	* testsuite/ld-xtensa/lcall.d: New file.
	* testsuite/ld-xtensa/lcall.exp: Remove file.
	* testsuite/ld-xtensa/xtensa.exp (coalesce, diff_overflow)
	(lcall): New tests.