AVX-512: Added i1 type handling for calling conventions.

i1 type is a legal type on AVX-512 and can be passed as parameter or return value.
i1 is promoted to i8 on return and to i32 for call arguments (i8 is also promoted to i32 here).
The result code is similar to the previous X86 targets, where i1 is allways promoted to i8.

llvm-svn: 237350