i2c: xlp9xx: Driver for Netlogic XLP9XX/5XX I2C controller

Add an I2C bus driver i2c-xlp9xx.c to support the I2C block in the
XLP9xx/XLP5xx MIPS SoC. Update Kconfig and Makefile to add the
CONFIG_I2C_XLP9XX option.

Signed-off-by: Subhendu Sekhar Behera <sbehera@broadcom.com>
Signed-off-by: Jayachandran C <jchandra@broadcom.com>
Reviewed-by: Ray Jui <rjui@broadcom.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>