OMAP3 clock: move DPLL bypass rate calculation into omap2_get_dpll_rate()

Removes the clksel-based DPLL rate handling from the OMAP3 clock tree.
In its place, omap2_get_dpll_rate() now has code to determine whether the DPLL
is bypassed.  This obsoletes several clocks, which are removed by this patch.

Signed-off-by: Paul Walmsley <paul@pwsan.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>