Fix bugs in X1000/X1500 and add X1830 pinctrl driver v2.

[Zhou Yanjie]

v1->v2:
1.Modify "nemc_" to "emc_" because X1000 has only one regular externel
  memory controller that does not support nand flash.
2.Add pinctrl drivers for the SPI flash controller (SFC) of X1000
  and X1500.
3.Add pinctrl driver for the synchronous serial interface (SSI)
  of X1000.
4.Add pinctrl bindings and pinctrl drivers for X1830 SoC.