vk_descriptor_pool: Initial implementation

Create a large descriptor pool where we allocate all our descriptors
from. It has to be wide enough to support any pipeline, hence its large
numbers.

If the descritor pool is filled, we allocate more memory at that moment.
This way we can take advantage of permissive drivers like Nvidia's that
allocate more descriptors than what the spec requires.

src/video_core/CMakeLists.txt

@@ -157,6 +157,8 @@ if (ENABLE_VULKAN)
         renderer_vulkan/maxwell_to_vk.h
         renderer_vulkan/vk_buffer_cache.cpp
         renderer_vulkan/vk_buffer_cache.h
+        renderer_vulkan/vk_descriptor_pool.cpp
+        renderer_vulkan/vk_descriptor_pool.h
         renderer_vulkan/vk_device.cpp
         renderer_vulkan/vk_device.h
         renderer_vulkan/vk_image.cpp