i2c: exynos: add support for HSI2C module on Exynos7

The HSI2C module on Exynos7 differs in the transfer status
bits. Transfer status bits were moved to INT_ENABLE and
INT_STATUS registers

This patch adds support for the HSI2C module on Exynos7.
1. Implementes a "hw" field in the variant struct to distinguish
   the hardware.
2. Updates the dt-new compatible in dt-binding documenation

Signed-off-by: Naveen Krishna Chatradhi <ch.naveen@samsung.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>