[RISCV][GISel] Support unaligned-scalar-mem. (#108905)
We need to set the required alignment to 8 with unaligned-scalar-mem. If we don't do this, the legalizer will try to lower the unaligned load/store and the lower code will call allowsMemoryAccess to verify what its supposed to do. allowsMemoryAccess will say the unaligned access is allowed. So the legalizer gives up.
