[RISCV] Improve constant materialization by using a sequence that end… (#66943)

…s with 2 addis in some cases.

If the lower 13 bits are something like 0x17ff, we can first materialize
it as 0x1800 followed by an addi to subtract a small offset. This might
be cheaper to materialize since the constant ending in 0x1800 can use a
simm12 immediate for its final addi.