MdeModulePkg/EhciDxe: factor out EhcIsDebugPortInUse()

MdeModulePkg/EhciDxe: factor out EhcIsDebugPortInUse()

The EhcReset(), EhcGetRootHubPortStatus() and EhcDriverBindingStart()
functions need to see whether the host controller (or a specific port on
the host controller) can be accessed, dependent on the controller having
(or the specific port being) an in-use debug port. Because the condition
isn't simple, extract it to a separate function.

Cc: Ruiyu Ni <ruiyu.ni@intel.com>
Cc: Star Zeng <star.zeng@intel.com>
Suggested-by: Star Zeng <star.zeng@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Star Zeng <star.zeng@intel.com>