bcm63xx: don't build CRAMFS

Don't build the CRAMFS file system module in the kernel, and save some bytes.

No bcm63xx board needs this obsolete file system, neither those ones using
the Redboot bootloader (liveboxes). Thus, there is no need to build it, since it has
been replaced long time ago by squashfs.

Signed-off-by: Daniel Gonzalez <dgcbueu@gmail.com>

SVN-Revision: 36616