Update predefined versions

There wasn't much feedback on the newsgroup so I've implemented the suggested changes. Please give some feedback if those changes are OK.

* Consistent naming: SoftFP --> SoftFloat (on ARM SoftFP != SoftFloat)
                     HardFP --> HardFloat
* DOC: ARM_Thumb means any Thumb version
* Add ARM_Thumb2 / ARM_Thumb1 (necessary when writing Thumb ASM)
  Thumb1 is still in use in the famous ARM7TDMI which is slowly being
  replaced by Cortex M3 now. (Those are microcontrollers)
* ARM/ARM64 fix reference regarding AARCH (AARCH is an arm8 term
  but ARM is also defined for ARM7,6,5...)
* Remove MIPS32: We should have *32 variants either for all
  architectures or for none.
* Remove MIPS_NoFloat: This should be a generic version D_NoFloat
  or it shouldn't be defined at all.
* D_X32: Add a note that defined both D_X32 and X86_64 is valid/expected
* D_LP64: We only talk about pointers, this is not the C LP64 data
model!