nvk: advertize KHR_relaxed_block_layout

Test run totals: Passed: 16/32 (50.0%) Failed: 0/32 (0.0%) Not supported: 16/32 (50.0%) Warnings: 0/32 (0.0%)

Not supported is: "Physical storage buffer pointers not supported", so waiting for VK_KHR_buffer_device_address.