USB: HCD: Add dummy functions when host mode disabled

If CONFIG_USB is disabled in the defconfig and some hcd
function is invoked by other drivers, then it can lead
to compilation failure. Fix this by adding appropriate
dummy functions in case of CONFIG_USB disabled.

Change-Id: I3e4110cd90c926af9ee81b6f981889c53ae5b039
Signed-off-by: Ajay Agarwal <ajaya@codeaurora.org>