KVM: x86/mmu: Apply retry protection to "fast nTDP unprotect" path

KVM: x86/mmu: Apply retry protection to "fast nTDP unprotect" path

Move the anti-infinite-loop protection provided by last_retry_{eip,addr}
into kvm_mmu_write_protect_fault() so that it guards unprotect+retry that
never hits the emulator, as well as reexecute_instruction(), which is the
last ditch "might as well try it" logic that kicks in when emulation fails
on an instruction that faulted on a write-protected gfn.

Add a new helper, kvm_mmu_unprotect_gfn_and_retry(), to set the retry
fields and deduplicate other code (with more to come).

Link: https://lore.kernel.org/r/20240831001538.336683-9-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>