drivers/i2c/i2c_dw.c: rewrite for PCI(e) support

The legacy PCI support in the DesignWare I2C driver is replaced with
the new PCIe support. The Intel Quark X1000 SoC and the galileo board
configurations are updated accordingly.

Signed-off-by: Charles E. Youse <charles.youse@intel.com>