package/libssh: needs MMU support

Fixes
http://autobuild.buildroot.net/results/405/40562b1b68bb7c57a37907eb16fcae88448f5bc6/
http://autobuild.buildroot.net/results/194/194ee885dd195706bded3ed524ff1685f4f6d4b5/
http://autobuild.buildroot.net/results/55c/55c00309bc7497529d28e48dce14299adeb11ede/
http://autobuild.buildroot.net/results/5d4/5d4e40fc4bb9c5a7ede26434c3d6ab325c631ecc/
http://autobuild.buildroot.net/results/8be/8bead9cfd826843482ccc37e9c1290b8774c8de0/
http://autobuild.buildroot.net/results/401/40100e6b07c3057ba427975ffdf3c3834c6fb385/
http://autobuild.buildroot.net/results/d70/d7083a8b197e1833ddaa30620ec1037ed15ec0ce/
http://autobuild.buildroot.net/results/6a2/6a20f29e65f446165b21cba3d55294e6ea446ff2/
http://autobuild.buildroot.net/results/718/718fdc0e5c67fd5cb1bceaec97f39285c159fbda/



Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>