video encode: support more DPB image formats and usage limitations

[clemy]

This allows to use all image formats for DPB images. The video encode tests are not accessing the images, so they can support any image format. Further, as the test cases do not access the images, only the usage flag VK_IMAGE_USAGE_VIDEO_ENCODE_DPB_BIT_KHR is necessary. I am not aware that implementations must support VK_IMAGE_USAGE_TRANSFER_SRC_BIT, but maybe I am wrong here?

Affects: dEQP-VK.video.encode.*

[CLAassistant]

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