Type legalizer for masked gather and scatter intrinsics.

Full type legalizer that works with all vectors length - from 2 to 16, (i32, i64, float, double).

This intrinsic, for example
void @llvm.masked.scatter.v2f32(<2 x float>%data , <2 x float*>%ptrs , i32 align , <2 x i1>%mask )
requires type widening for data and type promotion for mask.

Differential Revision: http://reviews.llvm.org/D13633

llvm-svn: 255629