drm/panfrost: Increase the AS_ACTIVE polling timeout

Experience has shown that 1ms is sometimes not enough, even when the GPU
is running at its maximum frequency, not to mention that an MMU operation
might take longer if the GPU is running at a lower frequency, which is
likely to be the case if devfreq is active.

Let's pick a significantly bigger timeout value (1ms -> 100ms) to be on
the safe side.

v5:
* New patch

Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>
Reviewed-by: Steven Price <steven.price@arm.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210630062751.2832545-17-boris.brezillon@collabora.com