binutils/testsuite: Permit the reuse of dump patterns

binutils/testsuite: Permit the reuse of dump patterns

Complement commit 89210bdc8fd2 ("GAS: Permit the reuse of dump
patterns"), <https://sourceware.org/ml/binutils/2010-07/msg00269.html>,
and commit ef2b5578f693 ("MIPS: Enable NewABI tests for SDE targets"),
<https://sourceware.org/ml/binutils/2012-08/msg00017.html>, and like the
GAS and LD versions make the binutils version of `run_dump_test' also
support the `dump' keyword, for reusing dump patterns between tests.

	binutils/
	* testsuite/lib/utils-lib.exp (run_dump_test): Handle the `dump'
	option.