timer: Pass function down to initialization routines

In preparation for removing more macros, pass the function down to the
initialization routines instead of doing it in macros.

Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: John Stultz <john.stultz@linaro.org>
Cc: Stephen Boyd <sboyd@codeaurora.org>
Signed-off-by: Kees Cook <keescook@chromium.org>