Kernel: Move Spinlock functions back to arch independent Locking folder

Now that the Spinlock code is not dependent on architectural specific
code anymore, we can move it back to the Locking folder. This also means
that the Spinlock implemenation is now used for the aarch64 kernel.

Kernel/CMakeLists.txt

@@ -202,6 +202,7 @@ set(KERNEL_SOURCES
     MiniStdLib.cpp
     Locking/LockRank.cpp
     Locking/Mutex.cpp
+    Locking/Spinlock.cpp
     Net/Intel/E1000ENetworkAdapter.cpp
     Net/Intel/E1000NetworkAdapter.cpp
     Net/NE2000/NetworkAdapter.cpp
@@ -333,7 +334,6 @@ if ("${SERENITY_ARCH}" STREQUAL "i686" OR "${SERENITY_ARCH}" STREQUAL "x86_64")
 
         Arch/x86/common/ScopedCritical.cpp
         Arch/x86/common/SmapDisabler.cpp
-        Arch/x86/common/Spinlock.cpp
     )
 
     set(KERNEL_SOURCES
@@ -464,7 +464,6 @@ else()
         Arch/aarch64/SafeMem.cpp
         Arch/aarch64/ScopedCritical.cpp
         Arch/aarch64/SmapDisabler.cpp
-        Arch/aarch64/Spinlock.cpp
         Arch/aarch64/vector_table.S
 
         # Files from base Kernel
@@ -475,6 +474,8 @@ else()
         Graphics/Console/BootFramebufferConsole.cpp
         Graphics/Console/GenericFramebufferConsole.cpp
 
+        Locking/Spinlock.cpp
+
         Memory/AddressSpace.cpp
         Memory/AnonymousVMObject.cpp
         Memory/InodeVMObject.cpp