This PR aims to make firesim support VC707 for subsequent work.
Currently, only the support-vc707.md document has been added, and subsequent documents and other file modifications will continue to follow up.
The subsequent migrating work is roughly expected to proceed as follows:

1. Imitate the process of generating bitstream for the u250 board by the firesim buildbitstream command to generate vc707 bitstream.
2. After generating the bitstream, try to manually program the vc707 board and test it.
3. After the manual test is completed, try to write the automated process into the firesim python program.