boards: arm: mchp: Configure VCI pins as GPIOs only when required

Default alternate function for the MEC15xx VCI pins makes them
HW-controlled.
Most common scenario is that pins are used as GPIOs, however
there are still some board designs where HW-controlled is desired.

Signed-off-by: Jose Alberto Meza <jose.a.meza.arellano@intel.com>