ACPI/IORT: Remove leftover ACPI_IORT_SMMU_V3_PXM_VALID guard

The conditional ACPI_IORT_SMMU_V3_PXM_VALID guard around
arm_smmu_v3_set_proximity() was added to manage a cross tree
ACPICA merge dependency; with ACPICA changes merged in:

commit c9442300 ("ACPICA: iasl: Update to IORT SMMUv3
disassembling")

the guard has become useless. Remove it.
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Acked-by: Hanjun Guo <hanjun.guo@linaro.org>
Cc: Hanjun Guo <hanjun.guo@linaro.org>
Cc: Sudeep Holla <sudeep.holla@arm.com>
Cc: Ganapatrao Kulkarni <ganapatrao.kulkarni@cavium.com>

drivers/acpi/arm64/iort.c

@@ -968,7 +968,7 @@ static bool __init arm_smmu_v3_is_coherent(struct acpi_iort_node *node)
 	return smmu->flags & ACPI_IORT_SMMU_V3_COHACC_OVERRIDE;
 }
 
-#if defined(CONFIG_ACPI_NUMA) && defined(ACPI_IORT_SMMU_V3_PXM_VALID)
+#if defined(CONFIG_ACPI_NUMA)
 /*
  * set numa proximity domain for smmuv3 device
  */