Add support for converting bitfiles to memory configuration files with Vivado

[tswilliams]

Currently in order to convert bitfiles to MCS files (which is required to load them onto the Serenity Artix PROMs), I run the following TCL command:

write_cfgmem -format mcs -size 32 -interface SPIx4 -loadbit {up 0x00000000 "/path/to/top.bit"} -file "/path/to/result.mcs" }

From my perspective, It would be useful to integrate this functionality (creation of mem config files) into the IPBB workflow - e.g. by adding a new command such as ipbb vivado mem-file

It would be even better if the resulting MCS file could be included in the tarball created by the ipbb vivado package command