ARM: rmobile: Add support for Renesas RZ/N1 SoC

The RZ/N1 is a family of SoC devices from Renesas, featuring:

* ARM Cortex-A7 CPU (single/dual core) and/or Cortex-M3
* Integrated SRAM up to 6MB
* Integrated gigabit ethernet switch
* Optional DDR2/3 controller
* I2C, SPI, UART, NAND, QSPI, SDIO, USB, CAN, RTC, LCD

Add basic support for this family, modeled on the existing RZA1.

Signed-off-by: Ralph Siemsen <ralph.siemsen@linaro.org>
Reviewed-by: Marek Vasut <marek.vasut+renesas@mailbox.org>