vkCreate*Pipeline slows down for larger pipelines

[samikhawaja]

vkCreate*Pipeline slows down when the size of the pipeline is bigger than 128KB. Pipelines large than 128KB cause a separate allocation of default pool size of 256KB. Also for each pipeline creation the pool gpumemory is mapped and unmapped.

This can be resolved by increasing the default size of the pool and keeping the memory mapped after usage. The mapped memory can be reused by the new vkCreate*Pipeline.