Testing LNCFCMOCS values on non-render engines is tricky. The values in
those registers are lost on RC6, which means that if users of non-render
engines want to see the proper values, they need to obtain a forcewake
and execute something on render (relying on it to restore the values)
before using non-render engine.
Previous version of the test did exactly that - we were relying on the
fact that we're taking forcewake (hidden by intel_register_access_init,
even though the test is not doing any mmio accesses) before iterating
through engines (and render is before other engines, so job done).
I really hope that this is not an ABI and those registers are not used
on non-render in any way. Let's limit testing LNCFCMOCS to render
engine only.
The other non-render issue is that when we're using I915_EXEC_BSD, we
can't be sure which BSD ring we'll end up executing on. Let's
explicitly select BSD1 and BSD2 in our tests.
While we're here, let's also remove the duplicated code and add some
structure by extracting moving more content into subtests.
We're only doing tests that involve "dirtying" the registers for the
render engine - since it's the only one that has those registers in its
context.

v2: Do not skip all BSD engines, test non-default contexts on render
only, change names in CI extended.testlist

Cc: Arkadiusz Hiler <arkadiusz.hiler@intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: David Weinehall <david.weinehall@linux.intel.com>
Cc: Łukasz Kałamarz <lukasz.kalamarz@intel.com>
Signed-off-by: Michał Winiarski <michal.winiarski@intel.com>
Reviewed-by: Łukasz Kałamarz <lukasz.kalamarz@intel.com>