MdePkg/Rng: Add GetRngGuid() to RngLib

The EFI_RNG_PROTOCOL can use the RngLib. The RngLib has multiple
implementations, some of them are unsafe (e.g. BaseRngLibTimerLib).
To allow the RngDxe to detect when such implementation is used,
add a GetRngGuid() function to the RngLib.

Signed-off-by: Pierre Gondois <pierre.gondois@arm.com>
Reviewed-by: Liming Gao <gaoliming@byosoft.com.cn>
Reviewed-by: Sami Mujawar <sami.mujawar@arm.com>
Acked-by: Ard Biesheuvel <ardb@kernel.org>
Tested-by: Kun Qin <kun.qin@microsoft.com>

MdeModulePkg/Library/BaseRngLibTimerLib/BaseRngLibTimerLib.inf

@@ -29,6 +29,10 @@
 
 [Packages]
   MdePkg/MdePkg.dec
+  MdeModulePkg/MdeModulePkg.dec
+
+[Guids]
+  gEdkiiRngAlgorithmUnSafe
 
 [LibraryClasses]
   BaseLib