MdePkg: Add read stable counter operation for LoongArch

Add LoongArch gets stable counter ASM function.

BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=4584

Cc: Michael D Kinney <michael.d.kinney@intel.com>
Cc: Liming Gao <gaoliming@byosoft.com.cn>
Cc: Zhiguang Liu <zhiguang.liu@intel.com>
Signed-off-by: Chao Li <lichao@loongson.cn>
Acked-by: Michael D Kinney <michael.d.kinney@intel.com>
Reviewed-by: Liming Gao <gaoliming@byosoft.com.cn>

MdePkg/Include/Library/BaseLib.h

@@ -339,6 +339,18 @@ AsmCpucfg (
   OUT UINT32  *Data
   );
 
+/**
+  Gets the timer count value.
+
+  @param[] VOID
+  @retval  timer count value.
+
+**/
+UINTN
+AsmReadStableCounter (
+  VOID
+  );
+
 #endif // defined (MDE_CPU_LOONGARCH64)
 
 //