allwinner: Introduce names for SoC IDs

We will soon make more use of the Allwinner SoC ID, to differentiate the
platform setup.
Introduce definitions to avoid dealing with magic numbers and make the
code more readable.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
diff --git a/plat/allwinner/common/sunxi_bl31_setup.c b/plat/allwinner/common/sunxi_bl31_setup.c
index 7e11cec..b56b9ee 100644
--- a/plat/allwinner/common/sunxi_bl31_setup.c
+++ b/plat/allwinner/common/sunxi_bl31_setup.c
@@ -68,13 +68,13 @@
 	uint16_t soc_id = sunxi_read_soc_id();
 
 	switch (soc_id) {
-	case 0x1689:
+	case SUNXI_SOC_A64:
 		soc_name = "A64/H64/R18";
 		break;
-	case 0x1718:
+	case SUNXI_SOC_H5:
 		soc_name = "H5";
 		break;
-	case 0x1728:
+	case SUNXI_SOC_H6:
 		soc_name = "H6";
 		break;
 	default: