usb: phy: omap-usb3: Improve DPLL parameter lookup code

Use a mapping table (dpll_map) to match the possible system clock rates
to the appropriate DPLL parameters.

Introduce a function "omap_usb3_get_dpll_params()" that will
return the matching DPLL parameters for the given clock rate.

Also, bail out on phy init if DPLL locking fails.

Signed-off-by: Roger Quadros <rogerq@ti.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>