update_cpu_features: tweak generic csky model

A truly generic model is not possible for csky, but with this weak, it covers
148 of 151 models. I think that's Good Enough.

lib/std/Target/csky.zig

@@ -2575,7 +2575,7 @@ pub const cpu = struct {
         .name = "generic",
         .llvm_name = "generic",
         .features = featureSet(&[_]Feature{
-            .btst16,
+            .e2,
         }),
     };
     pub const @"i805": CpuModel = .{

tools/update_cpu_features.zig

@@ -2037,6 +2037,13 @@ const targets = [_]ArchTarget{
                 .flatten = true,
             },
         },
+        .model_overrides = &.{
+            .{
+                .llvm_name = "generic",
+                .extra_deps = &.{"e2"},
+                .omit_deps = &.{"btst16"},
+            },
+        },
     },
     .{
         .zig_name = "hexagon",