board/BuR/common: rename "usbupdate" environment to "usbscript"

usbupdate in real does allways load some script from usb-storage and execute
it, on all B&R targets.

So we do following 2 things:
- rename it to what it really does
- move it from boards to common environment

Signed-off-by: Hannes Petermaier <oe5hpm@oevsv.at>
diff --git a/include/configs/kwb.h b/include/configs/kwb.h
index 7798b80..d1c745e 100644
--- a/include/configs/kwb.h
+++ b/include/configs/kwb.h
@@ -80,10 +80,6 @@
 	"run loadromfs; " \
 	"tftp ${loadaddr} arimg && go ${loadaddr}; " \
 	"puts 'networkboot failed!';\0" \
-"usbupdate=echo updating u-boot from usb ...; " \
-	"usb start; " \
-	"fatload usb 0 0x80000000 updateubootusb.img && source; " \
-	"puts 'usbupdate failed!'\0" \
 "netscript=echo running script from network (tftp) ...; " \
 	"tftp 0x80000000 netscript.img && source; " \
 	"puts 'netscript load failed!'\0" \
@@ -101,7 +97,7 @@
 #endif /* !CONFIG_SPL_BUILD*/
 
 #define CONFIG_BOOTCOMMAND \
-	"run usbupdate;"
+	"run usbscript;"
 #define CONFIG_BOOTDELAY		0
 
 /* undefine command which we not need here */