v4l2: fix mistake when using fewer number of outputbuffer

fix the random ASSERT fail of v4l2decode
tests: DecodeStreamOutputDmabuf refine, use createEglImageFromHandle
tests: distinguish external texture (dma_buf) required by glsl shader

dma_buf texture is considered as external buffer in mesa,
it requires 'samplerExternalOES' in glsl shader
testscripts: add different psnr value for yamidecode and yamiencode