boards: Disable NET on platforms without NETDEVICES

None of these platforms enabled a networking devices, and disabled
CMD_NET. Given that we used to gate network support on CMD_NET rather
than NET, we disable CONFIG_NET on these platforms now.

Signed-off-by: Tom Rini <trini@konsulko.com>
---
Cc: Simon Glass <sjg@chromium.org>
Cc: Heinrich Schuchardt <xypron.glpk@gmx.de>
Cc: Matthias Winker <matthias.winker@de.bosch.com>
Cc: Philip Oberfichtner <pro@denx.de>
Cc: Minkyu Kang <mk7.kang@samsung.com>
Cc: Jaehoon Chung <jh80.chung@samsung.com>
Cc: Patrice Chotard <patrice.chotard@foss.st.com>
Cc: Patrick Delaunay <patrick.delaunay@foss.st.com>
Cc: Sergey Temerkhanov <s.temerkhanov@gmail.com>