imx: s/docs\/README.imximage/doc\/README.imximage/g

Fixed typo for doc/README.imximage on respective imximage.cfg files.

Cc: Tom Rini <trini@konsulko.com>
Cc: Stefano Babic <sbabic@denx.de>
Cc: Fabio Estevam <fabio.estevam@nxp.com>
Acked-by: Peng Fan <peng.fan@nxp.com>
Signed-off-by: Jagan Teki <jagan@amarulasolutions.com>
diff --git a/board/freescale/mx6ullevk/imximage.cfg b/board/freescale/mx6ullevk/imximage.cfg
index 3c219fa..80cb038 100644
--- a/board/freescale/mx6ullevk/imximage.cfg
+++ b/board/freescale/mx6ullevk/imximage.cfg
@@ -3,7 +3,7 @@
  *
  * SPDX-License-Identifier:	GPL-2.0+
  *
- * Refer docs/README.imxmage for more details about how-to configure
+ * Refer doc/README.imximage for more details about how-to configure
  * and create imximage boot image
  *
  * The syntax is taken as close as possible with the kwbimage