[ARM] realview: add automatic selection of versatile clk

The realview init code is calling the versatile clk init code.

Signed-off-by: Jean-Christophe DUBOIS <jcd@tribudubois.net>
[CORE] net: exclude net parameters if NET is not selected.

Signed-off-by: Jean-Christophe DUBOIS <jcd@tribudubois.net>