tests: allow tests programs to be installed

Install test programs is useful in cross compilation case.  By default
the behavior is the same and test programs aren't installed in $bindir.
If --enable-install-test-programs is set then test programs are
installed in $bindir.

Signed-off-by: Benjamin Gaignard <benjamin.gaignard@linaro.org>
Signed-off-by: Rob Clark <robdclark@gmail.com>