arm: vf610: add enet1 support

This patch contains several changes required for second Ethernet
(enet1/RMII1) port on vf610
- ANADIG PLL5 control definitions required for Ethernet RMII1 clock
- Secondary Ethernet (enet1) MAC RMII1 base address definition
- RMII1 iomux definitions
- VF610_PAD_PTA6__RMII0_CLKOUT iomux definition required for
  internal (e.g. crystal-less) Ethernet clocking.

Signed-off-by: Marcel Ziswiler <marcel@ziswiler.com>
[stefan@agner.ch: regrouped patch]
Signed-off-by: Stefan Agner <stefan@agner.ch>