Generating .mcs file from .bit or .bin file

You can use write_cfgmem from Vivado tcl command or srec_cat from srecord package.

Using write_cfgmem

vivado -mode tcl
Vivado% write_cfgmem -format MCS -size 16 -interface SPIx4 -loadbit "up 0 /path/to/a.bit" /path/to/output.mcs

Or save it in a .tcl and run it.

Using srec_cat

$ srec_cat -Output_Block_Size=16 /tmp/a.bit -Binary -o /tmp/a.hex -Intel