cpu/arm7_common: Fix thread_yield_higher in ISR
cpu/arm7_common: Fix thread_yield_higher in ISR

thread_yield_higher() in interrupt context must not yield immediately, but at
the end of the ISR. This commit fixes the behavior.

kaspar030/RIOT,miri64/RIOT,rfuentess/RIOT,kaspar030/RIOT,rfuentess/RIOT,jasonatran/RIOT,josephnoir/RIOT,kYc0o/RIOT,authmillenon/RIOT,RIOT-OS/RIOT,josephnoir/RIOT,jasonatran/RIOT,OlegHahm/RIOT,mtausig/RIOT,yogo1212/RIOT,rfuentess/RIOT,josephnoir/RIOT,yogo1212/RIOT,rfuentess/RIOT,kaspar030/RIOT,OlegHahm/RIOT,basilfx/RIOT,OTAkeys/RIOT,ant9000/RIOT,OlegHahm/RIOT,kaspar030/RIOT,toonst/RIOT,toonst/RIOT,aeneby/RIOT,kYc0o/RIOT,basilfx/RIOT,x3ro/RIOT,authmillenon/RIOT,yogo1212/RIOT,aeneby/RIOT,OTAkeys/RIOT,yogo1212/RIOT,x3ro/RIOT,mtausig/RIOT,aeneby/RIOT,mtausig/RIOT,mtausig/RIOT,cladmi/RIOT,basilfx/RIOT,OlegHahm/RIOT,toonst/RIOT,yogo1212/RIOT,aeneby/RIOT,jasonatran/RIOT,miri64/RIOT,kYc0o/RIOT,miri64/RIOT,x3ro/RIOT,cladmi/RIOT,authmillenon/RIOT,basilfx/RIOT,toonst/RIOT,smlng/RIOT,kYc0o/RIOT,smlng/RIOT,yogo1212/RIOT,authmillenon/RIOT,RIOT-OS/RIOT,ant9000/RIOT,jasonatran/RIOT,OTAkeys/RIOT,RIOT-OS/RIOT,smlng/RIOT,cladmi/RIOT,ant9000/RIOT,toonst/RIOT,OTAkeys/RIOT,OlegHahm/RIOT,x3ro/RIOT,x3ro/RIOT,josephnoir/RIOT,ant9000/RIOT,RIOT-OS/RIOT,smlng/RIOT,kYc0o/RIOT,ant9000/RIOT,rfuentess/RIOT,kaspar030/RIOT,miri64/RIOT,authmillenon/RIOT,cladmi/RIOT,OTAkeys/RIOT,basilfx/RIOT,aeneby/RIOT,authmillenon/RIOT,miri64/RIOT,jasonatran/RIOT,josephnoir/RIOT,RIOT-OS/RIOT,mtausig/RIOT,smlng/RIOT,cladmi/RIOT