i2c: designware_i2c: Add ic_enable_status to ic_regs struct

Add the ic_enable_status register to the i2c_regs struct. Additionally
the register offsets are added, to better check, if the offset matches
the register description in the datasheet.

Signed-off-by: Stefan Roese <sr@denx.de>
Cc: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Cc: Marek Vasut <marex@denx.de>
Cc: Heiko Schocher <hs@denx.de>