KVM: x86: Break CONFIG_KVM_X86's direct dependency on KVM_INTEL || KVM_AMD

KVM: x86: Break CONFIG_KVM_X86's direct dependency on KVM_INTEL || KVM_AMD

Rework CONFIG_KVM_X86's dependency to only check if KVM_INTEL or KVM_AMD
is selected, i.e. not 'n'.  Having KVM_X86 depend directly on the vendor
modules results in KVM_X86 being set to 'm' if at least one of KVM_INTEL
or KVM_AMD is enabled, but neither is 'y', regardless of the value of KVM
itself.

The documentation for def_tristate doesn't explicitly state that this is
the intended behavior, but it does clearly state that the "if" section is
parsed as a dependency, i.e. the behavior is consistent with how tristate
dependencies are handled in general.

  Optionally dependencies for this default value can be added with "if".

Fixes: ea4290d77bda ("KVM: x86: leave kvm.ko out of the build if no vendor module is requested")
Cc: stable@vger.kernel.org
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-ID: <20241118172002.1633824-3-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>