mmc: sh_mobile_sdhi: properly document R-Car versions

Replace hardcoded values with meaningful names and document what we
know.

Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Reviewed-by: Simon Horman <horms+renesas@verge.net.au>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

drivers/mmc/host/sh_mobile_sdhi.c

@@ -39,6 +39,12 @@
 
 #define EXT_ACC           0xe4
 
+#define SDHI_VER_GEN2_SDR50	0x490c
+/* very old datasheets said 0x490c for SDR104, too. They are wrong! */
+#define SDHI_VER_GEN2_SDR104	0xcb0d
+#define SDHI_VER_GEN3_SD	0xcc10
+#define SDHI_VER_GEN3_SDMMC	0xcd10
+
 #define host_to_priv(host) container_of((host)->pdata, struct sh_mobile_sdhi, mmc_data)
 
 struct sh_mobile_sdhi_of_data {
@@ -109,14 +115,14 @@ static void sh_mobile_sdhi_sdbuf_width(struct tmio_mmc_host *host, int width)
 	 *	sh_mobile_sdhi_of_data :: dma_buswidth
 	 */
 	switch (sd_ctrl_read16(host, CTL_VERSION)) {
-	case 0x490C:
+	case SDHI_VER_GEN2_SDR50:
 		val = (width == 32) ? 0x0001 : 0x0000;
 		break;
-	case 0xCB0D:
+	case SDHI_VER_GEN2_SDR104:
 		val = (width == 32) ? 0x0000 : 0x0001;
 		break;
-	case 0xCC10: /* Gen3, SD only */
-	case 0xCD10: /* Gen3, SD + MMC */
+	case SDHI_VER_GEN3_SD:
+	case SDHI_VER_GEN3_SDMMC:
 		if (width == 64)
 			val = 0x0000;
 		else if (width == 32)