i2c: nomadik: support elder Nomadiks

The Nomadik I2C block was introduced with the Nomadik STn8815
SoC (the STn8810 incidentally is identical to the one named
i2c-stu300.c). However as developments have only been tested
on the DB8500 family, it was not properly working with the
STn8815 anymore.

Rectify this by adding some vendor variant data in the same
manner as other PrimeCells, and switch code path depending
on version.

Tested on the S8815 Nomadik dongle.

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>