powerpc/mm/64s: Only use slbfee on CPUs that support it

The slbfee instruction was only added in ISA 2.05 (Power6), it's not
supported on older CPUs. We don't have a CPU feature for that ISA
version though, so just use the ISA 2.06 feature flag.

Fixes: e15a4fea4d ("powerpc/64s/hash: Add some SLB debugging tests")
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/mm/slb.c

@@ -66,6 +66,9 @@ static void assert_slb_presence(bool present, unsigned long ea)
 
 	WARN_ON_ONCE(mfmsr() & MSR_EE);
 
+	if (!cpu_has_feature(CPU_FTR_ARCH_206))
+		return;
+
 	asm volatile(__PPC_SLBFEE_DOT(%0, %1) : "=r"(tmp) : "r"(ea) : "cr0");
 
 	WARN_ON(present == (tmp == 0));