KVM: x86/mmu: Fold rmap_recycle into rmap_add

[ Upstream commit 68be1306 ]

Consolidate rmap_recycle and rmap_add into a single function since they
are only ever called together (and only from one place). This has a nice
side effect of eliminating an extra kvm_vcpu_gfn_to_memslot(). In
addition it makes mmu_set_spte(), which is a very long function, a
little shorter.

No functional change intended.

Signed-off-by: David Matlack <dmatlack@google.com>
Message-Id: <20210813203504.2742757-3-dmatlack@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Stable-dep-of: 604f5332 ("KVM: x86/mmu: add missing update to max_mmu_rmap_size")
Signed-off-by: Sasha Levin <sashal@kernel.org>