pc: q35: Bump max_cpus to 1024

pc: q35: Bump max_cpus to 1024

Since KVM_MAX_VCPUS is currently defined to 1024 for x86 as shown in
arch/x86/include/asm/kvm_host.h, update QEMU limits to the same number.

In case KVM could not support the specified number of vcpus, QEMU would
return the following error message:

  qemu-system-x86_64: kvm_init_vcpu: kvm_get_vcpu failed (xxx): Invalid argument

Also, keep max_cpus at 288 for machine version 8.0 and older.

Cc: Igor Mammedov <imammedo@redhat.com>
Cc: Daniel P. Berrangé <berrange@redhat.com>
Cc: Michael S. Tsirkin <mst@redhat.com>
Cc: Julia Suvorova <jusual@redhat.com>
Reviewed-by: Igor Mammedov <imammedo@redhat.com>
Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
Message-Id: <20230607205717.737749-3-suravee.suthikulpanit@amd.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>