Add support for differentiating between protected (a.k.a. private, a.k.a.
encrypted) memory and normal (a.k.a. shared) memory for VMs that support
protected guest memory, e.g. x86's SEV.  Provide and manage a common
bitmap for tracking whether a given physical page resides in protected
memory, as support for protected memory isn't x86 specific, i.e. adding a
arch hook would be a net negative now, and in the future.

Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Sean Christopherson <seanjc@google.com>
Cc: Vishal Annapurve <vannapurve@google.com>
Cc: Ackerley Tng <ackerleytng@google.com>
cc: Andrew Jones <andrew.jones@linux.dev>
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Cc: Michael Roth <michael.roth@amd.com>
Reviewed-by: Itaru Kitayama <itaru.kitayama@fujitsu.com>
Tested-by: Carlos Bilbao <carlos.bilbao@amd.com>
Originally-by: Michael Roth <michael.roth@amd.com>
Signed-off-by: Peter Gonda <pgonda@google.com>
Co-developed-by: Sean Christopherson <seanjc@google.com>
Link: https://lore.kernel.org/r/20240223004258.3104051-5-seanjc@google.comSigned-off-by: Sean Christopherson <seanjc@google.com>