linuxkpi: Split <linux/compiler.h>

On Linux, they split the content into three headers:

1. <linux/compiler.h>
2. <linux/compiler_types.h>
3. <linux/compiler_attributes.h>

The first includes the second, which includes the third.

<linux/compiler_types.h> is also included on the compiler command line
by default! I added that to the compilation flags of the DRM drivers.
This allowed me to drop at least one:

#ifdef __FreeBSD
#include <linux/compiler.h>
#endif

Note that our copy of <linux/compiler.h> contains definitions which are
not defined by Linux' <linux/compiler.h>. I left them alone.

Reviewed by: emaste
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D54495