ARM: simplify CPSR handling

ARM: simplify CPSR handling

Stash a pointer to the CPSR in the "struct arm", to help get rid
of the (common) references to its index in the register cache.

This removes almost all references to CPSR offsets outside of the
toplevel ARM code ... except a pair related to the current ARM11
"simulator" logic (which should be removable soonish).

This is a net minor code shrink of a few hundred bytes of object
code, and also makes the code more readable.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>