add missing ISR_ATTR to methods called from isrs

[arneboe]

Add some isr attrs that where missing and causing crashes when cache was disabled.

[someweisguy]

I'm surprised that the static inline functions were causing crashes. They're supposed to be inlined to avoid cache crashes. :(

Excellent catch on dmx_driver_is_installed(). I feel like a dummy for missing it! :)

[arneboe]

I am not sure if the static inlines where the problem.
I followed all methods from the isr callbacks and added the attribute. Could very well be that only the dmx_driver_is_installed was the problem.