i2c-pnx.c: Remove duplicated i2c.h

The platforms using i2c-pnx.c both defined a duplicated i2c.h (used nowhere
else). This patch removes those and integrates the contents into the driver
itself.

Signed-off-by: Roland Stigge <stigge@antcom.de>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Wolfram Sang <w.sang@pengutronix.de>