igt: Use COND_BBEND for busy spinning on gen9

gen9+ introduces a cmdparser for the BLT engine which copies the
incoming BB to a kmd owned buffer for submission (to prevent changes
being made after the bb has been safely scanned). This breaks the
spin functionality because it relies on changing the submitted spin
buffers in order to terminate them.

Instead, for gen9+, we change the semantics by introducing a COND_BB_END
into the infinite loop, to wait until a memory flag (in anothe bo) is
cleared.

v2: Correct nop length to avoid overwriting bb_end instr when using
    a dependency bo (cork)
v3: fix conflicts on igt_dummyload (Mika)
v4: s/bool running/uint32_t running, fix r->delta (Mika)
v5: remove overzealous assert (Mika)
v6: rebase on top of lib changes (Mika)
v7: rework on top of public igt lib changes (Mika)
v8: rebase
v9: simplify by using bb end as conditional (Chris)

Signed-off-by: Jon Bloomfield <jon.bloomfield@intel.com> (v2)
Cc: Joonas Lahtinen <joonas.lahtinen@intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: Mika Kuoppala <mika.kuoppala@intel.com>
Signed-off-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>