updated the Bus Driver that is able to create all or one of its child handles on...

updated the Bus Driver that is able to create all or one of its child handles on each call to Start() not to create new child handle if RemainingDeviepath is the End of Device Path Node, per UEFI 2.3.

The others changes include:
1. Check RemainingDevicePath at beginning of Supported(), make sure it has been verified before Start() is called.
2. Check IO protocol firstly rather than EfiDevicePathProtocolGuid, reduce the times entering into Start() function because EfiDevicePathProtocolGuid existed on most of handle.
3. If no any child device is created on last time, and RemainingDevicePath is valid Uart Devcie path, go on creating child device handle based on this RemainingDevicePath.

git-svn-id: https://edk2.svn.sourceforge.net/svnroot/edk2/trunk/edk2@9262 6f19259b-4bc3-4df7-8a09-765794883524