[RISCV] Add +unaligned-scalar-mem to spacemit-x60 (#115125)

I can't find any official documentation on this, but from other
discussions[^1] and my own testing the spacemit-x60 seems to support
unaligned scalar loads and stores.

They seem to be performant, and just from a quick test we get a 2.45%
speedup on 500.perlbench_r on the Banana Pi F3[^2].

This would allow it to take advantage of #107548.

[^1]:
#110454 (comment)
[^2]: https://lnt.lukelau.me/db_default/v4/nts/32

Author: lukel97

llvm/lib/Target/RISCV/RISCVProcessors.td

@@ -476,7 +476,8 @@ def SPACEMIT_X60 : RISCVProcessorModel<"spacemit-x60",
                                         FeatureStdExtZicond,
                                         FeatureStdExtZvfh,
                                         FeatureStdExtZvkt,
-                                        FeatureStdExtZvl256b]),
+                                        FeatureStdExtZvl256b,
+                                        FeatureUnalignedScalarMem]),
                                        [TuneDLenFactor2,
                                         TuneOptimizedNF2SegmentLoadStore,
                                         TuneOptimizedNF3SegmentLoadStore,