Hello Yong,
My apologies for the inconveniences this is causing. As you pointed out the git://git.freescale.com repository was decommissioned, and its contents were moved to the following repositories:
github.com/NXP
github.com/NXPMicro
https://source.codeaurora.org/external/imx/
As for the imx-firmware packages in particular, the firmware-imx GIT repository new location is:
https://github.com/NXP/imx-firmware
I hope this helps!
Regards,