KVM: arm64: mte: Introduce VM_MTE_KVM VMA flag

Tag storage pages mapped by the host in a VM with MTE enabled are migrated
when they are first accessed by the guest. This introduces latency spikes
for memory accesses made by the guest.

Tag storage pages can be mapped in the guest memory when the VM_MTE VMA
flag is not set. Introduce a new VMA flag, VM_MTE_KVM, to stop tag storage
pages from being mapped in a VM with MTE enabled.

The flag is different from VM_MTE, because the pages from the VMA won't be
mapped as tagged in the host, and host's userspace can continue to access
the guest memory as Untagged. The flag's only function is to instruct the
page allocator to treat the allocation as tagged, so tag storage pages
aren't used. The page allocator will also try to reserve tag storage for
the new page, which can speed up stage 2 aborts further if the VMM has
accessed the memory before the guest. For example, qemu and kvmtool will
benefit from this change because the guest image is copied after the
memslot is created.