drivers: i2c: remove deprecated i2c_atmel_sam3 driver

The i2c_atmel_sam3 driver was deprecated at release 1.9, this commit
removes it. Also pinmux_dev_atmel_sam3x driver is removed.
i2c_atmel_sam3 was the last one which depended on it.

Signed-off-by: Piotr Mienkowski <piotr.mienkowski@gmail.com>