hw: x86_64: refactor Vm_session_component

On x86, the `Vm_session_component` obscured the differences between SVM
and VMX.

Separate the implementations, factor out common functionality and
address a number of long-standing issues in the process:

- Allocate nested page tables from Core_ram_allocator as a more suitable
  abstraction and account for the required memory, subtract the
  necessary amount of RAM from the session's `Ram_quota` *before*
  constructing the session object, to make sure that the memory
  allocated from the `Core_ram_allocator` is available from the VMM's
  RAM quota.
- Move the allocation of Vcpu_state and Vcpu_data into the Core::Vcpu
  class and use the Core RAM Allocator to allocate memory with a known
  physical address.
- Remove the fixed number of virtual CPUs and the associated reservation
  of memory by using a Registry for a flexible amount of vCPUs.

Issue #5221

repos/base/include/vm_session/connection.h

@@ -99,7 +99,7 @@ struct Genode::Vm_connection : Connection<Vm_session>, Rpc_client<Vm_session>
 	              long priority = Cpu_session::DEFAULT_PRIORITY,
 	              unsigned long affinity = 0)
 	:
-		Connection<Vm_session>(env, label, Ram_quota { 16*1024 }, Affinity(),
+		Connection<Vm_session>(env, label, Ram_quota { 5*1024*1024 }, Affinity(),
 		                       Args("priority=", Hex(priority), ", "
 		                            "affinity=", Hex(affinity))),
 		Rpc_client<Vm_session>(cap())