The use of the new types introduced for PowerPC MMA instructions need to be restricted.
We add a PowerPC function to SemaChecking.cpp checking that the given type is valid in a context in which we don't allow MMA types.
This function is called from various places in Sema where we want to prevent the use of these types.
Depends on D81748
Would this be a better comment for this function (since it may be confusing to say return true if the type is invalid but the function name is CheckPPCValidType?