framework: Only create one command pool per queue family
We only need to create one command pool per queue family, not per queue. Each command buffer created on a command pool for a queue family can be submitted to any queue on that queue family.
Here we fill in an array (t->vk.cmd_pool) where every queue can access an appropriate command pool for it's queue family. The queues that share the same family get assigned the same command pool in the array.
Recommended-by: @llandwerlin
Ref: !77 (comment 782934)