i2c-nomadik: depend on ARM_AMBA, not PLAT_NOMADIK

The gateware device has been used outside of the Nomadik world, using
the pci-amba bridge driver, so loosen the dependencies.

Signed-off-by: Alessandro Rubini <rubini@gnudd.com>
Acked-by: Giancarlo Asnaghi <giancarlo.asnaghi@st.com>
Tested-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Wolfram Sang <w.sang@pengutronix.de>