SDCC compatible patch for STM8 SPL V2.2.0

This adds SDCC compatibility to the most recent STM8 driver published by ST Micro at this time: V2.2.0 / 30-September-2014.

Compiler-specific syntax for inline asm and interrupt declaration has been added alongside the Cosmic, IAR and Raisonance versions.

The USE_STDPERIPH_DRIVER def that required editing stm8s.h to use has been changed to NO_STDPERIPH_DRIVER which can be defined externally to toggle this behaviour.