mx6sabre_common: Add Fastboot support

Tested basic fastboot commands, such as:

On the mx6qsabresd U-boot prompt:

=> fastboot 0

On the host PC:

$ fastboot getvar bootloader-version -i 0x0525
bootloader-version: U-Boot 2015.10-rc2-23960-g2462cce-dirty
finished. total time: 0.000s

$ fastboot reboot  -i 0x0525 --> board reboots fine.

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>

include/configs/mx6sabre_common.h

@@ -238,6 +238,12 @@
 #define CONFIG_G_DNL_VENDOR_NUM		0x0525
 #define CONFIG_G_DNL_PRODUCT_NUM	0xa4a5
 #define CONFIG_G_DNL_MANUFACTURER	"FSL"
+
+#define CONFIG_USB_FUNCTION_FASTBOOT
+#define CONFIG_CMD_FASTBOOT
+#define CONFIG_ANDROID_BOOT_IMAGE
+#define CONFIG_FASTBOOT_BUF_ADDR   CONFIG_SYS_LOAD_ADDR
+#define CONFIG_FASTBOOT_BUF_SIZE   0x07000000
 #endif
 
 #endif                         /* __MX6QSABRE_COMMON_CONFIG_H */