arm: rmobile: Add SILK board support

SILK is an entry level development board based on R-Car E2 SoC (R8A7794)

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

Signed-off-by: Vladimir Barinov <vladimir.barinov@cogentembedded.com>
Reviewed-by: Tom Rini <trini@ti.com>
Signed-off-by: Nobuhiro Iwamatsu <iwamatsu@nigauri.org>
8 files changed