checkpatch: forbid filesystem accesses from within the kernel.

Use of the sys_open/close/read/write system calls from within
kernel code is inappropriate, and now triggers errors.

Change-Id: I98e20513c257d0664684b7144585853f617d771a
Signed-off-by: Gregory Bean <gbean@codeaurora.org>
(cherry picked from commit ee62f2afcac1bcb180b2f0dddf2c8f5cda54bc5b)
Signed-off-by: Stepan Moskovchenko <stepanm@codeaurora.org>