nak: Add a nak_qmd_size_B() query

Also add a #define NAK_QMD_ALIGN_B for alignments.  The alignment is
always 256B and there's no evidence of that changing.

Reviewed-by: Mel Henning <mhenning@darkrefraction.com>
Backport-to: 25.2
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/36995>

src/nouveau/compiler/meson.build

@@ -65,6 +65,7 @@ _nak_bindings_rs = rust.bindgen(
     '--allowlist-type', 'nak_.*',
     '--allowlist-type', 'nouveau_ws_.*',
     '--allowlist-var', 'DRM_.*',
+    '--allowlist-var', 'NAK_.*',
     '--allowlist-var', 'NVIDIA_VENDOR_ID',
     '--allowlist-function', 'drm.*',
     '--allowlist-function', 'nak_.*',

src/nouveau/compiler/nak.h

@@ -251,6 +251,12 @@ struct nak_qmd_info {
    struct nak_qmd_cbuf cbufs[8];
 };
 
+#define NAK_QMD_ALIGN_B 256
+#define NAK_MAX_QMD_SIZE_B 256
+#define NAK_MAX_QMD_DWORDS (NAK_MAX_QMD_SIZE_B / 4)
+
+uint32_t nak_qmd_size_B(const struct nv_device_info *dev);
+
 void nak_fill_qmd(const struct nv_device_info *dev,
                   const struct nak_shader_info *info,
                   const struct nak_qmd_info *qmd_info,

src/nouveau/compiler/nak/qmd.rs

@@ -580,6 +580,27 @@ fn fill_qmd<Q: QMD>(info: &nak_shader_info, qmd_info: &nak_qmd_info) -> Q {
     qmd
 }
 
+#[no_mangle]
+pub extern "C" fn nak_qmd_size_B(dev: &nv_device_info) -> u32 {
+    let size_B = if dev.cls_compute >= clcdc0::BLACKWELL_COMPUTE_A {
+        size_of::<Qmd5_0>().try_into().unwrap()
+    } else if dev.cls_compute >= clcbc0::HOPPER_COMPUTE_A {
+        size_of::<Qmd4_0>().try_into().unwrap()
+    } else if dev.cls_compute >= clc6c0::AMPERE_COMPUTE_A {
+        size_of::<Qmd3_0>().try_into().unwrap()
+    } else if dev.cls_compute >= clc3c0::VOLTA_COMPUTE_A {
+        size_of::<Qmd2_2>().try_into().unwrap()
+    } else if dev.cls_compute >= clc0c0::PASCAL_COMPUTE_A {
+        size_of::<Qmd2_1>().try_into().unwrap()
+    } else if dev.cls_compute >= cla0c0::KEPLER_COMPUTE_A {
+        size_of::<Qmd0_6>().try_into().unwrap()
+    } else {
+        panic!("Unknown shader model");
+    };
+    assert!(size_B <= NAK_MAX_QMD_SIZE_B);
+    size_B
+}
+
 #[no_mangle]
 pub extern "C" fn nak_fill_qmd(
     dev: *const nv_device_info,