linuxkpi: Include <linux/list.h> and <linux/kernel.h> from <linux/mutex.h>

They are not really used in this header. However they are included in
Linux and at least the DRM drivers unfortunately rely on this namespace
pollution.

Reviewed by: manu
Approved by: manu
Differential Revision: https://reviews.freebsd.org/D37365

(cherry picked from commit 42bb5861162f071708406a8f70bcc6da5b832dc3)