[ARM] 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.

linux-omap source commit is 050684c18f2ea0b08fdd5233a0cd3c7f96e00a0e.

Signed-off-by: Paul Walmsley <paul@pwsan.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>