drm/panfrost: fix power transition timeout warnings

Increase the timeout value to prevent system logs on Amlogic boards flooding
with power transition warnings:

[   13.047638] panfrost ffe40000.gpu: shader power transition timeout
[   13.048674] panfrost ffe40000.gpu: l2 power transition timeout
[   13.937324] panfrost ffe40000.gpu: shader power transition timeout
[   13.938351] panfrost ffe40000.gpu: l2 power transition timeout
...
[39829.506904] panfrost ffe40000.gpu: shader power transition timeout
[39829.507938] panfrost ffe40000.gpu: l2 power transition timeout
[39949.508369] panfrost ffe40000.gpu: shader power transition timeout
[39949.509405] panfrost ffe40000.gpu: l2 power transition timeout

The 2000 value has been found through trial and error testing with devices
using G52 and G31 GPUs.

Fixes: 22aa1a20

 ("drm/panfrost: Really power off GPU cores in panfrost_gpu_power_off()")
Signed-off-by: Christian Hewitt <christianshewitt@gmail.com>
Reviewed-by: Steven Price <steven.price@arm.com>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Signed-off-by: Steven Price <steven.price@arm.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240322164525.2617508-1-christianshewitt@gmail.com