Documenation/laptops: rename and update hpfall.c

Dell kernel driver dell-smo8800 provides same freefall interface as hp_accel so
program hpfall.c works also on Dell laptops. So rename it to freefall.c.

Dell driver does not provide hp::hddprotect led so make sure that freefall.c
works also if hp::hddprotect does not exist in sysfs.

Additionally write info to syslog.

Signed-off-by: Pali Rohár <pali.rohar@gmail.com>
Cc: Sonal Santan <sonal.santan@gmail.com>
Acked-by: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>