* a workaround of loading kernel hang, simply pull pcie_reset pin low while booting kernel.
 * don't read gpio in checkboard.
 * init pcie if CONFIG_CMD_PCI defined.
 * change all mmc device opration to device 3.
this make user downgrade their uboot version, still can operate the correct device.
 * short auto-negotiation process loop from 10000 to 100