1. retire the FvbServiceLib. Directly locating FVB protocol to access interfaces.

1. retire the FvbServiceLib. Directly locating FVB protocol to access interfaces.
2. modify the method of getting right FVB protocol interface. move the notification event of FVB installation into variable driver. and also move ExitBootService event into variable driver.
3. use EFI_FVB2_WRITE_STATUS flag to distinct whether the FVB protocol supports writing operation or not.Currently, DxeCore installs FVB which has ~EFI_FVB2_WRITE_STATUS(that is, disable write) attrbiute. FvbRuntimeDxe driver should provide a full FVB protocol, which returns EFI_FVB2_WRITE_STATUS attribute to signify itself provide writable FVB protocol. So other modules which need write data by FVB protocol can locate it correctly.

git-svn-id: https://edk2.svn.sourceforge.net/svnroot/edk2/trunk/edk2@7835 6f19259b-4bc3-4df7-8a09-765794883524