Noncore dpll can enter autoidle state, in which case the rate calculation
fails.  Fixed by checking dpll mode instead of idle status.

Also, previously, the OMAP2xxx code returned the wrong value for the
DPLL rate under some conditions.  Move the CORE_CLK rate recalculation
to clock24xx.c:omap2xxx_clk_get_core_rate().

This patch is a collaboration between Tero Kristo <tero.kristo@nokia.com>
and Paul Walmsley <paul@pwsan.com>.  Thanks to Peter de Schrijver
<peter.de-schrijver@nokia.com> for help debugging and Kevin Hilman
<khilman@deeprootsystems.com> for reporting the OMAP2 build problems with
an earlier version of this patch.
Signed-off-by: Tero Kristo <tero.kristo@nokia.com>
Signed-off-by: Paul Walmsley <paul@pwsan.com>
Cc: Kevin Hilman <khilman@deeprootsystems.com>
Cc: Peter de Schrijver <peter.de-schrijver@nokia.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>