Kernel: Use nested namespace declarations in ACPI code

Kernel/ACPI/DynamicParser.cpp

@@ -8,8 +8,7 @@
 #include <Kernel/ACPI/Parser.h>
 #include <Kernel/Sections.h>
 
-namespace Kernel {
-namespace ACPI {
+namespace Kernel::ACPI {
 
 UNMAP_AFTER_INIT DynamicParser::DynamicParser(PhysicalAddress rsdp)
     : IRQHandler(9)
@@ -57,4 +56,3 @@ void DynamicParser::build_namespace()
 }
 
 }
-}