USB: EHCI: Allow more methods for overriding

Some EHCI compliant controllers may operate in Full-Speed only
mode. HCD_USB11 flag needs to be set instead of HCD_USB2 flag
for this reason. Allow controller drivers to override the
default hc_driver flags.

Some controller drivers may use root hub PM hooks to manage
the controller clocks and gpio. Allow controller drivers to
override bus_suspend and bus_resume methods.

Change-Id: I264b2173d0a48e31e581fa248b371e386c16823c
Signed-off-by: Pavankumar Kondeti <pkondeti@codeaurora.org>