change to make inline helpers truly inline [issue 6875] (#6898)

* change to make inline helpers truly inline [issue 6875]

* pulled the inline helpers out of the TWI class [issue 6875]

* removed some inlines causing issues [issue 6875]

* removed 2 more inlines from slave timeout section [issue 6875]

* removed 2 more inline attributes on public functions, moved twi_scl_valley up into the master section [issue 6875]

Author: Tech-TX