drm/i915/pvc: Reduce stack usage in reset selftest with extra blitter engine

PVC adds extra blitter engines (in the following patch). The reset
selftest has a local array on the stack which is sized by the number
of engines. The increase pushes the size of this array to the point
where it trips the 'stack too large' compile warning. This patch takes
the allocation of the stack and makes it dynamic instead.

v2 (MattR):
 - Minor cosmetic changes:  re-sort definition and allocate using
   kmalloc_array().  (Tvrtko)

Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
Signed-off-by: John Harrison <John.C.Harrison@Intel.com>
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Reviewed-by: José Roberto de Souza <jose.souza@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220505213812.3979301-7-matthew.d.roper@intel.com