Add vulkan renderer via libplacebo.

Simple usage:
$ ffplay -hwaccel vulkan foo.mp4

Use cuda to vulkan map:
$ ffplay -hwaccel cuda foo.mp4

Create vulkan instance by libplacebo, and enable debug:
$ ffplay -hwaccel vulkan \
	-vulkan_params create_by_placebo=1:debug=1 foo.mp4
Signed-off-by: Zhao Zhili <zhilizhao@tencent.com>