combining two taxonomy fields into one exposed filter dropdown
You can follow this using below step:


Go to Administration -> Structure -> Views
Edit your existing view or create new new. 
Add Filter for taxonomy for 'home' and 'away'
Click on "Rearrange" filter icon in Filter section
Click on "Create new filter group" and move filter "Home taxonomy" and "Away taxonomy" in new filter group. 
Select Operator as "Or" in new filter group and save the form.