OMAP4: DPLL cascading: Fix build error if interactive governor is disabled

DPLL cascading directly calls function from interactive governor
to limit max timer rate.
So build fails if interactive governor or whole CPUfreq is disabled in config.

This patch adds dummy cpufreq_interactive_set_timer_rate() function
in case if interactive governor is disabled.

Change-Id: I493c2df6934fc20493ce9476f3c8005c51f91731
Signed-off-by: Taras Kondratiuk <taras@ti.com>