cpu/intel/model_206ax: Use macro IS_IVY_CPU

Use existing macro instead of open coding magic numbers.
No functionality change.

Change-Id: If45f7f3f2b4226cedde6ff91b9848b9875f45f9f
Signed-off-by: Patrick Rudolph <patrick.rudolph@9elements.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/79148
Reviewed-by: Paul Menzel <paulepanter@mailbox.org>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Arthur Heymans <arthur@aheymans.xyz>

src/cpu/intel/model_206ax/model_206ax_init.c

@@ -212,7 +212,7 @@ static void configure_c_states(void)
 		/* Secondary Plane Current Limit */
 		msr = rdmsr(MSR_PP1_CURRENT_CONFIG);
 		msr.lo &= ~0x1fff;
-		if (cpuid_eax(1) >= 0x30600)
+		if (IS_IVY_CPU(cpu_get_cpuid()))
 			msr.lo |= PP1_CURRENT_LIMIT_IVB;
 		else
 			msr.lo |= PP1_CURRENT_LIMIT_SNB;