Kernel: Use nested namespace declarations in ACPI code

Kernel/ACPI/Initialize.cpp

@@ -9,8 +9,7 @@
 #include <Kernel/CommandLine.h>
 #include <Kernel/Sections.h>
 
-namespace Kernel {
-namespace ACPI {
+namespace Kernel::ACPI {
 
 UNMAP_AFTER_INIT void initialize()
 {
@@ -34,4 +33,3 @@ bool is_enabled()
 }
 
 }
-}