perf/arm-cmn: Move group validation data off-stack

With the value of CMN_MAX_DTMS increasing significantly, our validation
data structure is set to get quite big. Technically we could pack it at
least twice as densely, since we only need around 19 bits of information
per DTM, but that makes the code even more mind-bogglingly impenetrable,
and even half of "quite big" may still be uncomfortably large for a
stack frame (~1KB). Just move it to an off-stack allocation instead.

Signed-off-by: Robin Murphy <robin.murphy@arm.com>
Link: https://lore.kernel.org/r/0cabff2e5839ddc0979e757c55515966f65359e4.1638530442.git.robin.murphy@arm.com
Signed-off-by: Will Deacon <will@kernel.org>