Kernel: Remove the kmalloc_eternal heap :^)

This was a premature optimization from the early days of SerenityOS.
The eternal heap was a simple bump pointer allocator over a static
byte array. My original idea was to avoid heap fragmentation and improve
data locality, but both ideas were rooted in cargo culting, not data.

We would reserve 4 MiB at boot and only ended up using ~256 KiB, wasting
the rest.

This patch replaces all kmalloc_eternal() usage by regular kmalloc().

Kernel/Storage/ATA/AHCIController.h

@@ -23,7 +23,7 @@ class AHCIController final : public ATAController
     , public PCI::Device {
     friend class AHCIPortHandler;
     friend class AHCIPort;
-    AK_MAKE_ETERNAL
+
 public:
     UNMAP_AFTER_INIT static NonnullRefPtr<AHCIController> initialize(PCI::DeviceIdentifier const& pci_device_identifier);
     virtual ~AHCIController() override;

Kernel/Storage/ATA/IDEChannel.h

@@ -37,7 +37,7 @@ class IDEController;
 class IDEChannel : public RefCounted<IDEChannel>
     , public IRQHandler {
     friend class IDEController;
-    AK_MAKE_ETERNAL
+
 public:
     enum class ChannelType : u8 {
         Primary,

Kernel/Storage/ATA/IDEController.h

@@ -19,7 +19,6 @@ class AsyncBlockDeviceRequest;
 
 class IDEController final : public ATAController
     , public PCI::Device {
-    AK_MAKE_ETERNAL
 public:
     static NonnullRefPtr<IDEController> initialize(PCI::DeviceIdentifier const&, bool force_pio);
     virtual ~IDEController() override;

Kernel/Storage/RamdiskController.h

@@ -18,7 +18,6 @@ namespace Kernel {
 class AsyncBlockDeviceRequest;
 
 class RamdiskController final : public StorageController {
-    AK_MAKE_ETERNAL
 public:
 public:
     static NonnullRefPtr<RamdiskController> initialize();

Kernel/Storage/RamdiskDevice.h

@@ -16,7 +16,7 @@ class RamdiskController;
 class RamdiskDevice final : public StorageDevice {
     friend class RamdiskController;
     friend class DeviceManagement;
-    AK_MAKE_ETERNAL
+
 public:
     static NonnullRefPtr<RamdiskDevice> create(const RamdiskController&, NonnullOwnPtr<Memory::Region>&& region, int major, int minor);
     virtual ~RamdiskDevice() override;

Kernel/Storage/StorageController.h

@@ -22,7 +22,6 @@ namespace Kernel {
 class AsyncBlockDeviceRequest;
 class StorageDevice;
 class StorageController : public RefCounted<StorageController> {
-    AK_MAKE_ETERNAL
 
 public:
     virtual ~StorageController() = default;

Kernel/Storage/StorageManagement.h

@@ -19,7 +19,6 @@ namespace Kernel {
 
 class PartitionTable;
 class StorageManagement {
-    AK_MAKE_ETERNAL;
 
 public:
     StorageManagement();