kernel/kernel: Use correct initial PID for userland Process instances

Starts the process ID counter off at 81, which is what the kernel itself
checks against internally when creating processes. It's actually
supposed to panic if the PID is less than 81 for a userland process.

src/core/hle/kernel/kernel.cpp

@@ -112,7 +112,7 @@ struct KernelCore::Impl {
 
     void Shutdown() {
         next_object_id = 0;
-        next_process_id = 10;
+        next_process_id = Process::ProcessIDMin;
         next_thread_id = 1;
 
         process_list.clear();
@@ -153,9 +153,7 @@ struct KernelCore::Impl {
     }
 
     std::atomic<u32> next_object_id{0};
-    // TODO(Subv): Start the process ids from 10 for now, as lower PIDs are
-    // reserved for low-level services
-    std::atomic<u64> next_process_id{10};
+    std::atomic<u64> next_process_id{Process::ProcessIDMin};
     std::atomic<u64> next_thread_id{1};
 
     // Lists all processes that exist in the current session.

src/core/hle/kernel/process.h

@@ -120,6 +120,18 @@ struct CodeSet final {
 
 class Process final : public WaitObject {
 public:
+    enum : u64 {
+        /// Lowest allowed process ID for a kernel initial process.
+        InitialKIPIDMin = 1,
+        /// Highest allowed process ID for a kernel initial process.
+        InitialKIPIDMax = 80,
+
+        /// Lowest allowed process ID for a userland process.
+        ProcessIDMin = 81,
+        /// Highest allowed process ID for a userland process.
+        ProcessIDMax = 0xFFFFFFFFFFFFFFFF,
+    };
+
     static constexpr std::size_t RANDOM_ENTROPY_SIZE = 4;
 
     static SharedPtr<Process> Create(KernelCore& kernel, std::string&& name);