nitrogen6x_defconfig: add CONFIG_PCI_MSI
mx6: add CONFIG_PCIE_FORCE_GEN1

Add config option to force gen1 pcie speed

Signed-off-by: Troy Kisky <troy.kisky@boundarydevices.com>
nitrogen6x_defconfig: pcie: force gen1 speed

previous commit made gen1 selectable, now select it.

Signed-off-by: Troy Kisky <troy.kisky@boundarydevices.com>