OMAP3 clock: DPLL{1,2}_FCLK clksel can divide by 4

OMAP34xx ES2 TRM Delta G to H states that the divider for DPLL1_FCLK and
DPLL2_FCLK can divide by 4 in addition to dividing by 1 and 2. Encode this
into the OMAP3 clock framework.

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