i915_gpu_error.c build failure

[Patrick Welche]

amd64 kernels built without DIAGNOSTIC fail with

/usr/src/sys/external/bsd/drm2/dist/drm/i915/i915_gpu_error.c:608:8: error: 
implicit declaration of function 'cpu_intr_p' [-We
rror=implicit-function-declaration]
    if (cpu_intr_p() || cpu_softintr_p() ||

(Trying to figure out cpu.h inclusion difference but haven't found it...)

Cheers,

Patrick