common: add cache flush to imxtract function

A cache flush is required when an image is extracted that is required on another core.

Signed-off-by: Pieter Voorthuijsen <pieter.voorthuijsen@prodrive-technologies.com>
diff --git a/common/cmd_ximg.c b/common/cmd_ximg.c
index ae2714d..64b9186 100644
--- a/common/cmd_ximg.c
+++ b/common/cmd_ximg.c
@@ -247,6 +247,8 @@
 		puts("OK\n");
 	}
 
+	flush_cache(dest, len);
+
 	setenv_hex("fileaddr", data);
 	setenv_hex("filesize", len);