riscv: misaligned: factorize trap handling

riscv: misaligned: factorize trap handling

Since both load/store and user/kernel should use almost the same path and
that we are going to add some code around that, factorize it.

Signed-off-by: Clément Léger <cleger@rivosinc.com>
Reviewed-by: Alexandre Ghiti <alexghiti@rivosinc.com>
Link: https://lore.kernel.org/r/20250422162324.956065-2-cleger@rivosinc.com
Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com>