mfd: omap-usb-host: Get clocks based on hardware revision

Not all revisions have all the clocks so get the necessary clocks
based on hardware revision.

This should avoid un-necessary clk_get failure messages that were
observed earlier.

Also remove the dummy USB host clocks from the OMAP3 clock data.
These are no longer expected by the driver.

Acked-by: Mike Turquette <mturquette@linaro.org> [OMAP3 CLK data]
Acked-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Roger Quadros <rogerq@ti.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>