[RFC PATCH] drm.h: Fix DRM compilation with bare-metal toolchain.

[Dave Airlie]

> An ifdef in drm.h expects to be compiled with full-fledged Linux
> toolchain, but it's common to compile kernel with just bare-metal
> toolchain which doesn't define __linux__. So, also add __KERNEL__
> check.
Seems okay, pushed.

Dave.