tests/pc8: Fail harder

tests/pc8: Fail harder

If the test enviroment isn't properly set up we should fail the
testcase, since otherwise there's no way to make sure a feature
actually works.

To cut down on bug triaging time extract the basic test (which was
previously used to skip all subtests) into a "basic" subtest.

Also fail the test hard if the msr interface isn't available. And
switch all other check in setup_enviroment to igt_require.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=69838
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>