rt-tests: bump version to 0.89

With this change we're moving to the latest version of rt-tests.

Existing patches were updated so they apply on sources without errors and
warnings.

In "01-fix-build-system.patch" CFLAGS substitution was removed because
now external CFLAGS are accepted:
http://git.kernel.org/cgit/linux/kernel/git/clrkwllms/rt-tests.git/commit/?id=dfcef6e557b7980a33aa30b45bde196ed1780eb1



Signed-off-by: Alexey Brodkin <abrodkin@synopsys.com>
Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Cc: Peter Korsgaard <peter@korsgaard.com>
Cc: Arnout Vandecappelle <arnout@mind.be>
Cc: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>