vulkan: support buffer_from_host_ptr (#18467)
* vulkan: support buffer_from_host_ptr
* hacky use of buffer_from_host_ptr for directio
* disable buffer_from_host_ptr cap
* use external memory for ggml_vk_host_malloc, revert model loader changes
* disable external_memory_host for MoltenVK
* take buffer memory types into account
* don't use external_memory_host for ggml_vk_host_malloc
