SW4STM32 and SW4Linux fully supports the STM32MP1 asymmetric multicore Cortex/A7+M4 MPUs

   With System Workbench for Linux, Embedded Linux on the STM32MP1 family of MPUs from ST was never as simple to build and maintain, even for newcomers in the Linux world.
And, if you install System Workbench for Linux in System Workbench for STM32 you can seamlessly develop and debug asymmetric applications running partly on Linux, partly on the Cortex-M4.
You can get more information from the ac6-tools website and download two short videos (registration required) highlighting:

System Workbench for STM32

failed eclipse plug-in update to System Workbench for STM32 v1.11.0 release

I did just update the plugins on Windows 7 too, and it worked for me.

Do you use any proxy ? You can configure them in Window > Preferences > General > Network Connection

Otherwise, try to reload the update site :
1 - Go to Help > Install New Software...
2 - Click on the hyperlink “Available Software Sites”
3 - Select the System Workbench repository then push on Reload
4 - Try to update again.

Hope it works,