confidential guest support: Add kvm_init() and kvm_reset() in class

confidential guest support: Add kvm_init() and kvm_reset() in class

Different confidential VMs in different architectures all have the same
needs to do their specific initialization (and maybe resetting) stuffs
with KVM. Currently each of them exposes individual *_kvm_init()
functions and let machine code or kvm code to call it.

To facilitate the introduction of confidential guest technology from
different x86 vendors, add two virtual functions, kvm_init() and kvm_reset()
in ConfidentialGuestSupportClass, and expose two helpers functions for
invodking them.

Signed-off-by: Xiaoyao Li <xiaoyao.li@intel.com>
Message-Id: <20240229060038.606591-1-xiaoyao.li@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>