imx: fix USB boot mode detection for i.MX 6UL and 6ULL

Add the reserved boot mode used in the bmode command for i.MX 6UL
and 6ULL as introduced in commit 3fd9579085 ("imx: mx6ull: fix USB
bmode for i.MX 6UL and 6ULL").

Also replace BMODE_UART with BMODE_RESERVED, which is more appropriate.
Commit 96aac843b6 ("imx: Use IMX6_BMODE_* macros instead of numericals")
added macros for boot modes, in the process the reserved boot mode got
named BMODE_UART. We use the reserved boot mode in the bmode command to
let the boot ROM enter serial downloader recovery mode. But this is only
a side effect, the actual boot mode is reserved...

Signed-off-by: Stefan Agner <stefan.agner@toradex.com>

arch/arm/include/asm/mach-imx/sys_proto.h

@@ -69,8 +69,13 @@ enum imx6_bmode_emi {
 
 enum imx6_bmode {
 	IMX6_BMODE_EMI,
-	IMX6_BMODE_UART,
+#if defined(CONFIG_MX6UL) || defined(CONFIG_MX6ULL)
+	IMX6_BMODE_QSPI,
+	IMX6_BMODE_RESERVED,
+#else
+	IMX6_BMODE_RESERVED,
 	IMX6_BMODE_SATA,
+#endif
 	IMX6_BMODE_SERIAL_ROM,
 	IMX6_BMODE_SD,
 	IMX6_BMODE_ESD,

arch/arm/mach-imx/spl.c

@@ -42,7 +42,7 @@ u32 spl_boot_device(void)
 		break;
 		}
 	/* Reserved: Used to force Serial Downloader */
-	case IMX6_BMODE_UART:
+	case IMX6_BMODE_RESERVED:
 		return BOOT_DEVICE_UART;
 	/* SATA: See 8.5.4, Table 8-20 */
 	case IMX6_BMODE_SATA: