cmd/asm: add double precision comparision testcases for riscv64

Change-Id: If8e03dfdb332a22ec9c6a0021d7e7955520f3ddc
Reviewed-on: https://go-review.googlesource.com/c/go/+/702136
Reviewed-by: Mark Freeman <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>
Reviewed-by: Mark Ryan <[email protected]>
Reviewed-by: Joel Sing <[email protected]>
Reviewed-by: Michael Knyszek <[email protected]>

Author: mengzhuo

src/cmd/asm/internal/asm/testdata/riscv64.s

@@ -358,6 +358,11 @@ start:
 	FNMSUBD	F1, F2, F3, F4				// 4b82201a
 	FNMADDD	F1, F2, F3, F4				// 4f82201a
 
+	// 21.6: Double-Precision Floating-Point Compare Instructions
+	FEQD	F0, F1, X7				// d3a300a2
+	FLTD	F0, F1, X7				// d39300a2
+	FLED	F0, F1, X7				// d38300a2
+
 	// 21.7: Double-Precision Floating-Point Classify Instruction
 	FCLASSD	F0, X5					// d31200e2