drm/panfrost: increase readl_relaxed_poll_timeout values

Amlogic SoC devices report the following errors frequently causing excessive
dmesg log spam and early log rotataion, although the errors appear to be
harmless as everything works fine:

[    7.202702] panfrost ffe40000.gpu: error powering up gpu L2
[    7.203760] panfrost ffe40000.gpu: error powering up gpu shader

ARM staff have advised increasing the timeout values to eliminate the errors
in most normal scenarios, and testing with several different G31/G52 devices
shows 20000 to be a reliable value.

Fixes: f3ba9122 ("drm/panfrost: Add initial panfrost driver")
Suggested-by: Steven Price <steven.price@arm.com>
Signed-off-by: Christian Hewitt <christianshewitt@gmail.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/20201008141738.13560-1-christianshewitt@gmail.com

drivers/gpu/drm/panfrost/panfrost_gpu.c

@@ -325,13 +325,13 @@ void panfrost_gpu_power_on(struct panfrost_device *pfdev)
 	/* Just turn on everything for now */
 	gpu_write(pfdev, L2_PWRON_LO, pfdev->features.l2_present);
 	ret = readl_relaxed_poll_timeout(pfdev->iomem + L2_READY_LO,
-		val, val == pfdev->features.l2_present, 100, 1000);
+		val, val == pfdev->features.l2_present, 100, 20000);
 	if (ret)
 		dev_err(pfdev->dev, "error powering up gpu L2");
 
 	gpu_write(pfdev, SHADER_PWRON_LO, pfdev->features.shader_present);
 	ret = readl_relaxed_poll_timeout(pfdev->iomem + SHADER_READY_LO,
-		val, val == pfdev->features.shader_present, 100, 1000);
+		val, val == pfdev->features.shader_present, 100, 20000);
 	if (ret)
 		dev_err(pfdev->dev, "error powering up gpu shader");