meta: rename kernel to Magenta

arch/x86_64/pmap.c

@@ -9,7 +9,7 @@
 #include <kernel/types.h>
 #include <kernel/vm-object.h>
 #include <kernel/vm.h>
-#include <mango/status.h>
+#include <magenta/status.h>
 
 /* some helpful datasize constants */
 #define C_1GiB          0x40000000ULL

arch/x86_64/toolchain.cmake

@@ -1,5 +1,5 @@
 # the name of the target operating system
-set(CMAKE_SYSTEM_NAME Mango)
+set(CMAKE_SYSTEM_NAME Magenta)
 
 # which compilers to use for C and C++
 set(CMAKE_C_COMPILER   x86_64-elf-gcc)