Documentation: update .gitignore files

Add some missing files to .gitignore.
Push Documentation/.gitignore down into subdirectories.
Signed-off-by: Peter Foley <pefoley2@pefoley.com>
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

Documentation/.gitignore

-filesystems/dnotify_test
-laptops/dslm
-timers/hpet_example
-vm/hugepage-mmap
-vm/hugepage-shm
-vm/map_hugetlb
-

Documentation/arm/SH-Mobile/.gitignore

+vrl4

Documentation/filesystems/.gitignore

+dnotify_test

Documentation/laptops/.gitignore

+dslm
+freefall

Documentation/networking/timestamping/.gitignore

 timestamping
+txtimestamp
 hwtstamp_config

Documentation/prctl/.gitignore

+disable-tsc-ctxt-sw-stress-test
+disable-tsc-on-off-stress-test
+disable-tsc-test

Documentation/ptp/.gitignore

+testptp

Documentation/timers/.gitignore

+hpet_example

Documentation/vDSO/.gitignore

+vdso_test
+vdso_standalone_test_x86

Documentation/video4linux/.gitignore

-v4lgrab