ffmpeg 4.0.2 -> 4.1

This is a workaround for GPU hang on heavy convolution workload (> 10 GFLOPS).
e.g. ResNet101_DUC_HDC

For the long time task, vkWaitForFences() return without error but next call on
vkQueueSubmit() return -4, i.e. "VK_ERROR_DEVICE_LOST" and driver reports GPU hang.

Need more investigation on root cause of GPU hang and need to optimize convolution shader
to reduce process time.

cmake: introduce setup_vars scripts

* GAPI: Sobel 3x3 with FP32 input

* GAPI: Sobel 3x3 with FP32 input, v2

typo in kmeans doc

* avoid rounding errors

* imgproc: replace condition in matchTemplate