The clock debugfs code is large enough, and easy enough to separate,
that it deserves its own file which is compiled only when
CONFIG_DEBUG_FS is enabled.

Also, cleanup header file #includes that are no longer required.
Reviewed-by: Saravana Kannan <skannan@codeaurora.org>
Signed-off-by: Matt Wagantall <mattw@codeaurora.org>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
Signed-off-by: David Brown <davidb@codeaurora.org>