powerpc/test_emulate_step: Add negative tests for prefixed addi

testcases for `paddi` instruction to cover the negative case,
if R is equal to 1 and RA is not equal to 0, the instruction
form is invalid.
Signed-off-by: Balamuruhan S <bala24@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20200626095158.1031507-3-bala24@linux.ibm.com

arch/powerpc/lib/test_emulate_step.c

@@ -1130,6 +1130,16 @@ static struct compute_test compute_tests[] = {
 				.regs = {
 					.gpr[21] = 0,
 				}
+			},
+			/* Invalid instruction form with R = 1 and RA != 0 */
+			{
+				.descr = "RA = R22(0), SI = 0, R = 1",
+				.instr = TEST_PADDI(21, 22, 0, 1),
+				.flags = NEGATIVE_TEST,
+				.regs = {
+					.gpr[21] = 0,
+					.gpr[22] = 0,
+				}
 			}
 		}
 	}