product/rdn2: fix the num of RNF_PER_CHIP in cmn700 config data

RD-N2 Multichip platform variant contains four CPUs (RN-Fs) per chip.
Fix this count in the config data. In order to make this macro specific
to the Multichip variant (Cfg2), rename this macro to RNF_PER_CHIP_CFG2.

Signed-off-by: Vijayenthiran Subramaniam <vijayenthiran.subramaniam@arm.com>
Change-Id: Iaab9867a97aef6a9d2d8d3333ba9cbd2a06647df