kwbimage: Rename CONFIG_SYS_SPI_U_BOOT_OFFS to CONFIG_SYS_U_BOOT_OFFS

To use this offset for other boot device (like SDIO/MMC), lets rename
it to a more generic name. This will be used be the SDIO/MMC SPL boot
support for the A38x.

Signed-off-by: Stefan Roese <sr@denx.de>
Cc: Luka Perkov <luka.perkov@sartura.hr>
Cc: Dirk Eibach <eibach@gdsys.de>
diff --git a/tools/Makefile b/tools/Makefile
index 98414f7..db55bcf 100644
--- a/tools/Makefile
+++ b/tools/Makefile
@@ -117,8 +117,8 @@
 HOST_EXTRACFLAGS	+= -DCONFIG_FIT_SIGNATURE
 endif
 
-ifdef CONFIG_SYS_SPI_U_BOOT_OFFS
-HOSTCFLAGS_kwbimage.o += -DCONFIG_SYS_SPI_U_BOOT_OFFS=$(CONFIG_SYS_SPI_U_BOOT_OFFS)
+ifdef CONFIG_SYS_U_BOOT_OFFS
+HOSTCFLAGS_kwbimage.o += -DCONFIG_SYS_U_BOOT_OFFS=$(CONFIG_SYS_U_BOOT_OFFS)
 endif
 
 # MXSImage needs LibSSL