drm/panfrost: Tighten polling for soft reset and power on

In many cases, soft reset takes more than 1 microsecond, but definitely
less than 10; moreover in the poweron flow, tilers, shaders and l2 will
become ready (each) in less than 10 microseconds as well.

Even in the cases (at least on my platforms, rarely) in which those take
more than 10 microseconds, it's very unlikely to see both soft reset and
poweron to take more than 70 microseconds.

Shorten the polling delay to 10 microseconds to consistently reduce the
runtime resume time of the GPU.

As an indicative example, measurements taken on a MediaTek MT8195 SoC

Average runtime resume time in nanoseconds before this commit:
GDM, user selection up/down:            88435ns
GDM, Text Entry (typing user/password): 91489ns
GNOME Desktop, idling, GKRELLM running: 73200ns

After this commit:

GDM: user selection up/down:            26690ns
GDM: Text Entry (typing user/password): 27917ns
GNOME Desktop, idling, GKRELLM running:	25304ns

Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Reviewed-by: Steven Price <steven.price@arm.com>
Signed-off-by: Steven Price <steven.price@arm.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20231109102543.42971-3-angelogioacchino.delregno@collabora.com