Add OS_AbortTrap implementation

This supports all the load/store instructions, including FPA & VFP/NEON.
Most instructions are handled directly via the base version of the
AbortTrap API that was first implemented in RISC OS Select. However, to
properly cope with LDREX/STREX, and future support for prefetch aborts,
the API has been extended to allow the kernel to request that a block of
memory is mapped in with certain permissions. For LDREX/STREX the kernel
will then rewind the PC so that the instruction can be retried directly.

Test code in Dev/AbortTrap exists in order to allow checking of all
major functionality, along with code for building the code in a
softloadable module for easier/quicker testing.

s/MoreSWIs

@@ -533,6 +533,7 @@ RdArgs_SWICode ROUT
       Pull   "R4, R8, R9, lr"
       B      SLVK_SetV
 
+      EXPORT ErrorBlock_BadParameters
       MakeErrorBlock BadParameters
       MakeErrorBlock ArgRepeated
       ALIGN

s/MsgCode

@@ -43,6 +43,7 @@ TranslateError_VClear  ROUT
         CLRV
         Pull    "r4,PC"
 
+        EXPORT  TranslateError
 TranslateError  ROUT
         Push    "r4,LR"
         MOV     r4,#0