[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/thread.cpp

@@ -17,7 +17,7 @@ thread::thread(process &parent, uint8_t pri, uintptr_t rsp0) :
 	m_wait_data(0),
 	m_wait_obj(0)
 {
-	m_tcb.pml4 = parent.pml4();
+	parent.space().initialize_tcb(m_tcb);
 	m_tcb.priority = pri;
 
 	if (!rsp0)