midi: rename PITCH_WHEEL_CHANGE to PITCHWHEEL_CHANGE
sw/sublime: change cents to be a 32-bit integer

8-bit isn't enough and 32-bit is used in the internal freq
reg calculations
sw/midi: rename midi_note struct to midi

This will become a generic structure for all kinds of midi events
sw/midi: make callback struct generic
sw/midi: add support for pitchwheel changes