[kernel] Move page mapping into vm_space

vm_space no longer relies on page_manager to map pages during a page
fault. Other changes that come with this commit:

- C++ standard has been changed to C++17
- enum bitfield operators became constexpr
- enum bifrield operators can take a mix of ints and enum arguments
- added page table flags enum instead of relying on ints
- remove page_table::unmap_table and page_table::unmap_pages

scripts/templates/build.ninja.j2

@@ -51,7 +51,7 @@ asflags = $
     -I${srcroot}/src/include
 
 cflags = -std=c11
-cxxflags = -std=c++14
+cxxflags = -std=c++17
 libs =
 
 rule c