[sparkplug] Invert the ENABLE_SPARKPLUG condition formulation

Now that only ppc lacks support, state that explicitly s.t. it's clear
which platforms are still missing.

Bug: v8:11420
Change-Id: I22a91270aaa389fc27ce5c7a3f8e8b9c44f01eb4
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3497544
Auto-Submit: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Cr-Commit-Position: refs/heads/main@{#79340}

src/flags/flag-definitions.h

@@ -195,13 +195,11 @@ struct MaybeBoolFlag {
 #define ENABLE_CONTROL_FLOW_INTEGRITY_BOOL false
 #endif
 
-#if V8_TARGET_ARCH_IA32 || V8_TARGET_ARCH_X64 || V8_TARGET_ARCH_ARM64 ||     \
-    V8_TARGET_ARCH_ARM || V8_TARGET_ARCH_RISCV64 || V8_TARGET_ARCH_MIPS64 || \
-    V8_TARGET_ARCH_MIPS || V8_TARGET_ARCH_LOONG64 || V8_TARGET_ARCH_S390X
-#define ENABLE_SPARKPLUG true
-#else
-// TODO(v8:11421): Enable Sparkplug for other architectures
+#if V8_TARGET_ARCH_PPC || V8_TARGET_ARCH_PPC64
+// TODO(v8:11421): Enable Sparkplug for these architectures.
 #define ENABLE_SPARKPLUG false
+#else
+#define ENABLE_SPARKPLUG true
 #endif
 
 #if ENABLE_SPARKPLUG && !defined(ANDROID)