[RISCV] Set isReMaterializable for ORI, XORI

Reviewers: asb

Reviewed By: asb

Subscribers: asb, rbar, johnrusso, simoncook, sabuasal, niosHD, kito-cheng, shiva0217, zzheng, edward-jones, rogfer01, MartinMosbeck, brucehoult, the_o, rkruppe, PkmX, jocewei

Differential Revision: https://reviews.llvm.org/D57069

llvm-svn: 352008