[RISCV] Enable the LocalStackSlotAllocation pass support

For RISC-V, load/store(exclude vector load/store) instructions only
has a 12 bit immediate operand. If the offset is out-of-range, it
must make use of a temp register to make up this offset. If between
these offsets, they have a small(IsInt<12>) relative offset,
LocalStackSlotAllocation pass can find a value as frame base register's
value, and replace the origin offset with this register's value plus
the relative offset.

Reviewed By: craig.topper

Differential Revision: https://reviews.llvm.org/D98101