feat(asm): encode the arm64 Q-width FP load and store

FMOVQ routes through the MOV load/store machinery in the plain, post-index,
pre-index and static-symbol forms.  The Q width carries its size in the opc
field, so the store spelling is opc=10 and the access scales by sixteen;
both come from helpers now instead of the size exponent.  The static-symbol
form takes the toolchain's twelve-byte ADRP + ADD + access fallback with the
R_ADDRARM64 pair.  The register-to-register and immediate forms stay
rejected, matching the toolchain's own table.

Assisted-by: GLM 5.3 Flash

asm/kernels_differential_test.go

@@ -142,6 +142,7 @@ func TestDifferentialKernels(t *testing.T) {
 		{filepath.Join("..", "testdata", "verify", "forms_amd64.s"), "", false},
 		{filepath.Join("..", "testdata", "verify", "datarel_arm64.s"), "arm64", true},
 		{filepath.Join("..", "testdata", "verify", "divslash_arm64.s"), "arm64", true},
+		{filepath.Join("..", "testdata", "verify", "qmov_arm64.s"), "arm64", true},
 	} {
 		t.Run(filepath.Base(k.path), func(t *testing.T) {
 			src, err := os.ReadFile(k.path)