vulkan: Block-load Q3_K/Q6_K block data and subtract on 32b ints (#23056)

Q2_K/Q3_K/Q6_K do much better when using MMVQ on Intel BMG even
though they're only 2-byte aligned, and Q3_K still wins on
NVIDIA as well.

mesa isn't all that great at coalescing back-to-back loads from
alternating arrays, so we force it instead. Further, we can do
subtraction directly on a full int32_t rather than an i8vec4
with bit twiddling because the high bit is always free to start.

On Intel BMG on mesa, the switch to MMVQ provides an immediate
~57% perf increase in tg128 for unsloth/Qwen3.5-9B-GGUF:Q3_K and
~78% perf increase in tg128 for unsloth/Qwen3.5-9B-GGUF:Q6_K.

The futher switch to block loads leads to a ~24% perf increase in
tg128 for unsloth/Qwen3.5-9B-GGUF:Q3_K and a ~48% perf increase in
tg128 for unsloth/Qwen3.5-9B-GGUF:Q6_K.

Finally, Xe2 wins on MMVQ even for small k, so we take the NVIDIA
override for K quants on Xe2 as well.

ggml/src/ggml-vulkan/ggml-vulkan.cpp

@@ -8336,8 +8336,10 @@ static bool ggml_vk_should_use_mmvq(const vk_device& device, uint32_t m, uint32_
         return false;
     }
 
-    // General performance issue with q3_k and q6_k due to 2-byte alignment
-    if (src0_type == GGML_TYPE_Q3_K || src0_type == GGML_TYPE_Q6_K) {
+    // q6_k only has 2-byte alignment which makes it somewhat problematic,
+    // using MMVQ is only a win on Intel.
+    bool mmvq_q6 = device->vendor_id == VK_VENDOR_ID_INTEL;
+    if (src0_type == GGML_TYPE_Q6_K && !mmvq_q6) {
         return false;
     }
 
@@ -8349,7 +8351,7 @@ static bool ggml_vk_should_use_mmvq(const vk_device& device, uint32_t m, uint32_
     // Quantization overhead is not worth it for small k
     switch (device->vendor_id) {
     case VK_VENDOR_ID_NVIDIA:
-        if (src0_type == GGML_TYPE_Q2_K || src0_type == GGML_TYPE_IQ1_S || src0_type == GGML_TYPE_IQ1_M) {
+        if (src0_type == GGML_TYPE_Q2_K || src0_type == GGML_TYPE_Q3_K || src0_type == GGML_TYPE_IQ1_S || src0_type == GGML_TYPE_IQ1_M) {
             return true;
         }
 
@@ -8376,9 +8378,16 @@ static bool ggml_vk_should_use_mmvq(const vk_device& device, uint32_t m, uint32_
             return true;
         }
     case VK_VENDOR_ID_INTEL:
+        if (device->architecture == vk_device_architecture::INTEL_XE2) {
+            if (src0_type == GGML_TYPE_Q2_K || src0_type == GGML_TYPE_Q3_K || src0_type == GGML_TYPE_Q6_K) {
+                return true;
+            }
+        }
+
         if (device->driver_id == vk::DriverId::eIntelProprietaryWindows) {
-            // Intel Windows proprietary driver MMVQ performance is worse than fp16, see
-            // https://github.com/ggml-org/llama.cpp/issues/17628
+            // Intel Windows proprietary driver MMVQ performance for !Q2/Q3/Q6 is worse than fp16,
+            // see https://github.com/ggml-org/llama.cpp/issues/17628 and
+            // https://github.com/ggml-org/llama.cpp/pull/23056
             return false;
         }