aarch32-symbolic: Add SIMD register Indexes, factor registers into a module

[langston-barrett]

Like #443, but for AArch32 this time.

[langston-barrett]

FWIW, I checked the GHC Core for these definitions (using -ddump-simpl) and found that they really do compile down to integers (with the expected values, no less:

Data.Macaw.AArch32.Symbolic.Regs.v62 :: Int
[GblId,
 Unf=Unf{Src=<vanilla>, TopLvl=True,
         Value=True, ConLike=True, WorkFree=True, Expandable=True,
         Guidance=IF_ARGS [] 10 10}]
Data.Macaw.AArch32.Symbolic.Regs.v62 = ghc-prim:GHC.Types.I# 82#

-- snip --

v31
  :: Ctx.Index
       (MS.MacawCrucibleRegTypes SA.AArch32) (LCLM.LLVMPointerType 128)
[GblId,
 Unf=Unf{Src=<vanilla>, TopLvl=True,
         Value=True, ConLike=True, WorkFree=True, Expandable=True,
         Guidance=ALWAYS_IF(arity=0,unsat_ok=True,boring_ok=True)}]
v31
  = Data.Macaw.AArch32.Symbolic.Regs.v62
    `cast` (Sym (Data.Parameterized.Context.Unsafe.N:Index[0] -- snip -- ) )