Add define so user can omit AP_Motors bindings

[peterbarker]

No description provided.

[tpwrules]

Let's standardize the define names so future work can make the bindings generator do this automagically.

Proposal

• name is the singleton or other object name (e.g. AP::motors()) coming from the bindings.desc file
• sanitize the name according to the rules i.e. AP__motors__ (replacing any of :.<>()- with _)
• suffix _index to get symbol name (this what the generator does internally)
• get the "rename" name if available, otherwise continue with sanitized name
• substitute into AP_SCRIPTING_BINDING_%s_ENABLED the uppercased version of the name

[peterbarker]

Current names conform to Thomas' suggestions.

This PR saves ~5400 bytes on CubeOrange / Copter when both are removed.

[tridge]

please test for no change on some boards