[RISCV] Teach MatInt to use (ADD_UW X, (SLLI X, 32)) to materialize some constants.

If the high and low 32 bits are the same, we try to use
(ADD X, (SLLI X, 32)) but that only works if bit 31 is clear since
the low 32 bits will be sign extended.

If we have Zba we can use add.uw to zero the sign extended bits.

Reviewed By: reames, wangpc

Differential Revision: https://reviews.llvm.org/D159253