vulkan: Sync renderer for blit filters

A spa_node has callback both on the main and data thread, which can modify the internal state of vulkan_blit_state. Especially critical are functions, which might drop buffers currently in use. To mitigate this a read-write lock is used. The data thread shall try to aquire a read lock before accessing the buffers, while the main thread has to aquire exclusive access via a write lock before modifying the buffers.

Contains a mall cleanup naming the params via defines.