KVM: x86/mmu: Rename slot rmap walkers to add clarity and clean up code

Replace "slot_handle_level" with "walk_slot_rmaps" to better capture what
the helpers are doing, and to slightly shorten the function names so that
each function's return type and attributes can be placed on the same line
as the function declaration.

No functional change intended.

Link: https://lore.kernel.org/mm-commits/CAHk-=wjS-Jg7sGMwUPpDsjv392nDOOs0CtUtVkp=S6Q7JzFJRw@mail.gmail.com


Signed-off-by: Ben Gardon <bgardon@google.com>
Link: https://lore.kernel.org/r/20230202182809.1929122-2-bgardon@google.com


Signed-off-by: Sean Christopherson <seanjc@google.com>