lib: move strtobool() to kstrtobool()

lib: move strtobool() to kstrtobool()

Create the kstrtobool_from_user() helper and move strtobool() logic into
the new kstrtobool() (matching all the other kstrto* functions).
Provides an inline wrapper for existing strtobool() callers.

Signed-off-by: Kees Cook <[email protected]>
Cc: Joe Perches <[email protected]>
Cc: Andy Shevchenko <[email protected]>
Cc: Rasmus Villemoes <[email protected]>
Cc: Daniel Borkmann <[email protected]>
Cc: Amitkumar Karwar <[email protected]>
Cc: Nishant Sarmukadam <[email protected]>
Cc: Kalle Valo <[email protected]>
Cc: Steve French <[email protected]>
Cc: Michael Ellerman <[email protected]>
Cc: Heiko Carstens <[email protected]>
Cc: Martin Schwidefsky <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>