Bump timeouts for a couple gdb.reverse/*-precsave.exp tests

Bump timeouts for a couple gdb.reverse/*-precsave.exp tests

The buildbot shows that PPC64 and x86_64 builders, both native and
extended-remote gdbserver frequently timeout these tests.
until-precsave.exp times out on my x86_64 occasionally as well.
Inspecting the logs, we see that if we waited some more, the tests
would pass.

Simply bump until-precsave.exp timeouts further, and apply the same
treatment to step-precsave.exp.

gdb/testsuite/ChangeLog:
2015-08-06  Pedro Alves <palves@redhat.com>

	* gdb.reverse/step-precsave.exp: Use with_timeout_factor to
	increase timeout.
	* gdb.reverse/until-precsave.exp: Bump timeouts.