KVM: x86/mmu: Rename TDP MMU functions that handle shadow pages

Rename 3 functions in tdp_mmu.c that handle shadow pages:

  alloc_tdp_mmu_page()  -> tdp_mmu_alloc_sp()
  tdp_mmu_link_page()   -> tdp_mmu_link_sp()
  tdp_mmu_unlink_page() -> tdp_mmu_unlink_sp()

These changed make tdp_mmu a consistent prefix before the verb in the
function name, and make it more clear that these functions deal with
kvm_mmu_page structs rather than struct pages.

One could argue that "shadow page" is the wrong term for a page table in
the TDP MMU since it never actually shadows a guest page table.
However, "shadow page" (or "sp" for short) has evolved to become the
standard term in KVM when referring to a kvm_mmu_page struct, and its
associated page table and other metadata, regardless of whether the page
table shadows a guest page table. So this commit just makes the TDP MMU
more consistent with the rest of KVM.

No functional change intended.

Signed-off-by: David Matlack <dmatlack@google.com>
Message-Id: <20220119230739.2234394-6-dmatlack@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>