Incorrectly adjusted brakes could cause a vibration, but won't make the steering wobbly. If your tyre pressure is too high, this will make the steering light and the bike might feel less comfortable (because the tyre acts as part of the overall dampening of bumps), but it shouldn't affect how the bike tracks.

Worn bearings in the steering head can make your motorcycle very difficult to control. They should be checked for wear and correct adjustment.