Fix all-reduce int tests by host-registering memrefs.

Reduce amount of boiler plate to register host memory.

Summary: Fix all-reduce int tests by host-registering memrefs.

Reviewers: herhut

Reviewed By: herhut

Subscribers: clementval, mehdi_amini, rriddle, jpienaar, burmako, shauheen, antiagainst, nicolasvasilache, arpith-jacob, mgester, lucyrfox, liufengdb, Joonsoo, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D76563