[kernel] Move pml4 create/delete into vm_space

vm_space and page_table continue to take over duties from
page_manager:

- creation and deletion of address spaces / pml4s
- cross-address-space copies for endpoints
- taking over pml4 ownership from process

Also fixed the bug where the wrong process was being set in the cpu
data.

To solve: now the kernel process has its own vm_space which is not
g_kernel_space.

src/kernel/objects/process.h

@@ -19,8 +19,7 @@ public:
 	constexpr static size_t stack_size = 0x4000;
 
 	/// Constructor.
-	/// \args pml4  Root of the process' page tables
-	process(page_table *pml4);
+	process();
 
 	/// Destructor.
 	virtual ~process();
@@ -35,9 +34,6 @@ public:
 	/// Update internal bookkeeping about threads.
 	void update();
 
-	/// Get the process' page table root
-	page_table * pml4() { return m_pml4; }
-
 	/// Get the process' virtual memory space
 	vm_space & space() { return m_space; }
 
@@ -75,7 +71,6 @@ public:
 private:
 	uint32_t m_return_code;
 
-	page_table *m_pml4;
 	vm_space m_space;
 
 	kutil::vector<thread*> m_threads;