[MCA] Do not allocate space for DependenceEdge by default in DependencyGraphNode (NFC)

For each instruction from the input assembly sequence, DependencyGraph has a
dedicated node (DGNode). Outgoing edges (data, resource and memory dependencies)
are tracked as SmallVector<..., 8> for each DGNode in the graph. However, it's
rather unlikely that a usual input instruction will have approximately eight
dependent instructions. Below is my statistics for several RISC-V input
sequences:

Number of  | Number of nodes with
edges      | this # of edges
--------------------------------------------
         0 | 8239447
         1 | 464252
         2 | 6164
         3 | 6783
         4 | 939
         5 | 500
         6 | 545
         7 | 116
         8 | 2
         9 | 1
        10 | 1

Approximately the same distribution is produced by llvm-mca lit tests (even
modified ones with extra dependencies added).
On a rather big input asm sequences, the use of SmallVector<..., 8> dramatically
increases memory consumption without any need for it. In my case, replacing it
with SmallVector<...,0> reduces memory usage by ~28% or ~1700% of input file size
(2.2GB in absolute values).

There is no change in execution time, I verified it on mca lit-tests and on my big
test (execution time is ~30s in both cases).

Author: asi-sc

llvm/tools/llvm-mca/Views/BottleneckAnalysis.h

@@ -228,7 +228,7 @@ class DependencyGraph {
     unsigned Depth;
 
     DependencyEdge CriticalPredecessor;
-    SmallVector<DependencyEdge, 8> OutgoingEdges;
+    SmallVector<DependencyEdge, 0> OutgoingEdges;
   };
   SmallVector<DGNode, 16> Nodes;