Turbo mode corrections

[sonninnos]

Description

Sorted a few goofs in turbo mode behavior:

• Fixed d-pad allow option from being ignored if the overriding bind option was empty, as in when legacy port turbo was used instead, resulting in classic modes allowing d-pad always
• Prevented single button toggle from toggling multiple buttons in classic style when it is supposed to limit itself only to the defined single button
• Limited minimum turbo period value to 2, since 1 is utterly useless
• Cleaned up some outdated comments