clk: tests: Add test suites description

We start to have a few test suites, and we'll add more, so it will get
pretty confusing to figure out what is supposed to be tested in what
suite.

Let's add some comments to explain what setup they create, and what we
should be testing in every suite.

Tested-by: Alexander Stein <alexander.stein@ew.tq-group.com> # imx8mp
Tested-by: Marek Szyprowski <m.szyprowski@samsung.com> # exynos4210, meson g12b
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Link: https://lore.kernel.org/r/20220816112530.1837489-7-maxime@cerno.tech


Tested-by: Linux Kernel Functional Testing <lkft@linaro.org>
Tested-by: Naresh Kamboju <naresh.kamboju@linaro.org>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>