[IR][Verifier] Allow IntToPtrInst to be !dereferenceable

Summary:
Allow IntToPtrInst to carry !dereferenceable metadata tag.
This is valid since !dereferenceable can be only be applied to
pointer type values.

Change-Id: If8a6e3c616f073d51eaff52ab74535c29ed497b4

Subscribers: llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D64954

llvm-svn: 366826