OMAP4: SDP4430: Disable CMD_NFS

This patch fixes the SDB4430 build after commit 6d8962e8
by explicitly disabling CMD_NFS.

>From the commit message for "Switch from archive libraries to partial linking":

This commit reveals board configurations that exclude some features but
include source files that depend these disabled features in the build,
resulting in undefined symbols.  Known such cases include:

- disabling CMD_NET but not CMD_NFS;
- enabling CONFIG_OF_LIBFDT but not CONFIG_QE.

Signed-off-by: Dirk Behme <dirk.behme@googlemail.com>
Signed-off-by: Sandeep Paulraj <s-paulraj@ti.com>