hw/nvram/nrf51_nvm: Add nRF51 non-volatile memories

hw/nvram/nrf51_nvm: Add nRF51 non-volatile memories

The nRF51 contains three regions of non-volatile memory (NVM):
- CODE (R/W): contains code
- FICR (R): Factory information like code size, chip id etc.
- UICR (R/W): Changeable configuration data. Lock bits, Code
  protection configuration, Bootloader address, Nordic SoftRadio
  configuration, Firmware configuration.

Read and write access to the memories is managed by the
Non-volatile memory controller.

Memory schema:
 [ CPU ] -+- [ NVM, either FICR, UICR or CODE ]
          |      |
          \- [ NVMC ]

Signed-off-by: Steffen Görtz <contrib@steffen-goertz.de>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Tested-by: Joel Stanley <joel@jms.id.au>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Message-id: 20190201023357.22596-2-stefanha@redhat.com
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>