arm: rmobile: Add Porter board support

Porter is an entry level development board based on R-Car M2 SoC (R8A7791)

This commit supports the following peripherals:
- SCIF, I2C, Ethernet, QSPI, SD, USB Host

Signed-off-by: Vladimir Barinov <vladimir.barinov@cogentembedded.com>
Signed-off-by: Nobuhiro Iwamatsu <iwamatsu@nigauri.org>
9 files changed