dts: update mermory regions for nrf chips

According to nrf51 and nrf52 specifaction every peripheral is
assigned a fixed block of 0x1000 bytes. Due to that dts for
nrf51 and nrf52 chips have been updated.
The only exception is gpio for nrf52840 where gpio0 and gpio1
share the same memory regions. For this reason, the definition
of gpio for nrf52840 is different from the others.

Signed-off-by: Jakub Rzeszutko <jakub.rzeszutko@nordicsemi.no>