usb/gadget: fastboot: minor cleanup

- update static function
- additional debugging statements
- update "fastboot command" information
- add missing include file
- update spelling

Signed-off-by: Steve Rae <srae@broadcom.com>
diff --git a/common/cmd_fastboot.c b/common/cmd_fastboot.c
index 83fa7bd..909616d 100644
--- a/common/cmd_fastboot.c
+++ b/common/cmd_fastboot.c
@@ -30,7 +30,8 @@
 }
 
 U_BOOT_CMD(
-	fastboot,	1,	1,	do_fastboot,
-	"fastboot - enter USB Fastboot protocol",
-	""
+	fastboot,	1,	0,	do_fastboot,
+	"use USB Fastboot protocol",
+	"\n"
+	"    - run as a fastboot usb device"
 );