ARM: OMAP3: clock: use clk_features flags for omap3 DPLL4 checks

DPLL4 can't be reprogrammed on OMAP3430 ES1.0 due to hardware limitation.
Currently, the code does runtime omap_rev() check to see the chip it is
being executed on, instead, change this to use clk_features flags.
This avoids need for runtime omap_rev() checks.

Signed-off-by: Tero Kristo <t-kristo@ti.com>
Signed-off-by: Paul Walmsley <paul@pwsan.com>