buffer_cache: allocate sparse backing with device address support (#5233)

* buffer_cache: allocate sparse backing with device address support [skip ci]

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Human code/comment review and human-written PR text required before upstream submission.
Source integration: e6cf874a170c528068627bb43f2c6bc2e89e4375.
Original commits: 1e6bb5a6.

* buffer_cache: remove allocation comment after review [skip ci]

Remove the two-line comment requested in upstream PR #5233. No executable code changes.

Validation: exact diff review only; no rebuild or tests for comment removal.

AI-assisted edit by Codex.

src/video_core/buffer_cache/buffer_cache.cpp

@@ -285,7 +285,11 @@ void BufferCache::EnsureResident(const Buffer* arena, u64 first_block, u64 last_
         return;
     }
 
+    const vk::MemoryAllocateFlagsInfo alloc_flags = {
+        .flags = vk::MemoryAllocateFlagBits::eDeviceAddress,
+    };
     const vk::MemoryAllocateInfo alloc_info = {
+        .pNext = &alloc_flags,
         .allocationSize = resident_blocks << block_shift,
         .memoryTypeIndex = arena_memory_type_index,
     };