i2c: Add GXP SoC I2C Controller

The GXP SoC supports 10 I2C engines. Each I2C engine is completely
independent and can function both as an I2C master and I2C slave. The
I2C master can operate in a multi master environment. The engines support
a scalable speed from 8kHZ to 1.5 Mhz.

Signed-off-by: Nick Hawkins <nick.hawkins@hpe.com>
Reviewed-by: Joel Stanley <joel@jms.id.au>
Signed-off-by: Wolfram Sang <wsa@kernel.org>