The crc code doesn't handle anything really that could drop the
register state (by design so that we have less complexity). Which
means userspace may only start crc capture once the pipe is fully set
up.

With an i-g-t patch this will be the case, but there's still the
problem that this results in obscure unclaimed register write
failures. Which is a pain to debug.

So instead make sure we don't have the basic unclaimed register write
failure by grabbing runtime pm references. And reject completely
invalid requests with -EIO. This is still racy of course, but for a
test library we don't really care - if userspace shuts down the pipe
right afterwards the entire setup will be lost anyway.

v2: Put instead of get, spotted by Damien. Also explain the runtime pm
dance.

v3: There's really no need for rpm get/put since power_is_enabled only
checks software state (Damien).

References: https://bugs.freedesktop.org/show_bug.cgi?id=86092
Cc: Damien Lespiau <damien.lespiau@intel.com> (v2)
Tested-by: lu hua <huax.lu@intel.com>
Reviewed-by: Damien Lespiau <damien.lespiau@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>