Fix references to the documentation files

Many boot image configuration files refer to the
appropriate documentation file, but these references
contain typos in the directory and file name. Fix
them. Also fix reference to doc/README.SPL file.

Signed-off-by: Anatolij Gustschin <agust@denx.de>
Cc: Prafulla Wadaskar <prafulla@marvell.com>
Cc: Stefano Babic <sbabic@denx.de>
Acked-by: Stefano Babic <sbabic@denx.de>
diff --git a/doc/SPL/README.am335x-network b/doc/SPL/README.am335x-network
index e5a198f..9b63791 100644
--- a/doc/SPL/README.am335x-network
+++ b/doc/SPL/README.am335x-network
@@ -7,7 +7,7 @@
 
  I. Building the required images
   1. You have to enable generic SPL configuration options (see
-docs/README.SPL) as well as CONFIG_SPL_NET_SUPPORT,
+doc/README.SPL) as well as CONFIG_SPL_NET_SUPPORT,
 CONFIG_ETH_SUPPORT, CONFIG_SPL_LIBGENERIC_SUPPORT and
 CONFIG_SPL_LIBCOMMON_SUPPORT in your board configuration file to build
 SPL with support for booting over the network. Also you have to enable