Config fixes for gShield/gquintic

[thatch]

It looks like SPINDLE_SPEED_CHANGE_PER_MS isn't exposed as config but the other values in settings nearby are; I'm not sure if that's intentional or an oversight.

For purposes of making axes move, gquintic-d should be pretty similar to gquintic-c, right?

[giseburt]

Yeah, that's an oversight. There were breaking changes between rev C and D on the quintic. We can maybe remove the Rev C code now and make sure anyone who has a C gets a newer board.

[justinclift]

@giseburt So, should this be merged? 😄

[thatch]

This one is simply a build fix; I can do a separate PR for adding the config option; I would also like to change it to _PER_TICK to match the member variable and how it's actually used, and worth a separate discussion.