code/debug-int: Strip arm conditionals from sub-access-debug-var noise.

  * Many of these cases work now that we have floating-point SAPs
implemented.  For the rest, I'd rather see an undefined-function
for CONTEXT-FLOAT-REGISTER than a CASE-FAILURE with a bunch of
integers.  As such, enable all of them.
compiler/arm/{insts,float}: Introduce psudo-instructions for complex load/store.

  * These are wrappers for float load/store multiple instructions,
providing a simple (if limited) way to load or store a complex
float in a single instruction.

  * The underlying float load/store multiple instructions don't
conform to what the rest of our instruction definitions do in
terms of interface, nor is a conforming interface particularly
convenient, so they got left as-is.

  * And these instruction-macros perform NO error checking, so
they will be easy to misuse by accident.

  * But this gets us a full series of instructions for loading and
storing integer, float, and complex-float values, to match the set
of macros for moving such values between registers.
compiler/arm/cell, code/{,target-}defstruct: Unboxed float struct slots.

  * All of the unboxed float accessors share pretty much the same
structure (if you'll pardon the pun), so restructure the existing
(unboxed word) accessor into a macrolet, then expose hooks for the
changes required (memory access instructions, result-moving macros,
limitations on displacements in memory access) and use them to
also define the various floating-point (including complex) slot
accessors.
General comment and whitespace fixups for arm-port-related damage.

  * Just a few things found with canonicalize-whitespace and some
comments that were added over the course of the port that are no
longer useful.