vulkan: fix build for GGML_VULKAN_RUN_TESTS, add TFLOPS to logging

[jeffbolznv]

GGML_VULKAN_RUN_TESTS currently has build errors like:

ggml-vulkan.cpp(5251,5): error C2664: 'void ggml_vk_dispatch_pipeline(ggml_backend_vk_context *,vk_context &,vk_pipeline &,const std::initializer_list<vk::DescriptorBufferInfo> &,size_t,const void *,std::array<uint32_t,3>)': cannot convert argument 4 from 'initializer list' to 'const std::initializer_list<vk::DescriptorBufferInfo> &'
ggml-vulkan.cpp(5497,10): error C2039: 'staging': is not a member of 'ggml_backend_vk_context'

and runtime assertions like:

ggml-vulkan.cpp:2486: GGML_ASSERT(pipeline->descriptor_set_idx < pipeline->descriptor_sets.size()) failed

Fix these, and also add teraflops calculation to the matmul tests.