dm: i2c: Add a sandbox I2C driver

This driver includes some test features such as only supporting certain
bus speeds. It passes its I2C traffic through to an emulator.

Acked-by: Heiko Schocher <hs@denx.de>
Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
2 files changed