avfilter/vf_gblur_vulkan: add sizeV option

This commit added a sizeV option, integrated some identical operations
to a separate function, and updated the CGS for horizontal and vertical
respectively.

The following command is on how to apply sizeV option:

ffmpeg -init_hw_device vulkan -i input.264 -vf \
hwupload,gblur_vulkan=size=127:sigma=20:sizeV=3:sigmaV=0.5,hwdownload,format=yuv420p \
-y out.264
Signed-off-by: Wu Jianhua <jianhua.wu@intel.com>