TableGen: Allow NAME in template arguments in defm in multiclass

Summary:
NAME has already worked for def in a multiclass, since the (protoype)
record including its NAME variable is created before parsing the
superclasses. Since defm's do not have an associated single record,
support for NAME has to be implemented differently here.

Original test cases provided by Artem Belevich (tra)

Change-Id: I933b74f328c0ff202e7dc23a35b78f3505760cc9

Reviewers: arsenm, craig.topper, tra, MartinO

Subscribers: wdng, llvm-commits

Differential Revision: https://reviews.llvm.org/D43656

llvm-svn: 326700