ANDROID: GKI: hack up fs/sysfs/file.c to prevent GENKSYMS change

In commit cb1f69d5 ("sysfs: Add sysfs_emit and sysfs_emit_at to
format sysfs output") in 4.19.179, a #include <linux/mm.h> addition is
added to the fs/sysfs/file.c file, before sysfs.h is included in the
build.  This ends up causing a previously "UNKNOWN" symbol type
definition of struct vm_operations_struct to become "known" which
propagates to a CRC change for some sysfs symbol definitions.

To prevent all this mess, add a simple #ifndef to prevent the mm.h file
from being included when running the symbol tool, and all is fine.

Bug: 161946584
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>
Change-Id: Ibcc22bedc4f39d2ef49a52ebd7962a8dba5b0583