cpufreq: ti-cpufreq: Support additional am43xx platforms

Rather than letting the ti-cpufreq driver match against 'ti,am4372'
machine compatible during probe let's match against 'ti,am43' so that we
can support both 'ti,am4372' and 'ti,am438x' platforms which both match
to this compatible.

Signed-off-by: Dave Gerlach <d-gerlach@ti.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>