target/i386/kvm: Clean up error handling in kvm_arch_init()

target/i386/kvm: Clean up error handling in kvm_arch_init()

Currently, there're following incorrect error handling cases in
kvm_arch_init():
* Missed to handle failure of kvm_get_supported_feature_msrs().
* Missed to return when kvm_vm_enable_disable_exits() fails.
* MSR filter related cases called exit() directly instead of returning
  to kvm_init(). (The caller of kvm_arch_init() - kvm_init() - needs to
  know if kvm_arch_init() fails in order to perform cleanup).

Fix the above cases.

Signed-off-by: Zhao Liu <zhao1.liu@intel.com>
Reviewed-by: Zide Chen <zide.chen@intel.com>
Link: https://lore.kernel.org/r/20241106030728.553238-11-zhao1.liu@intel.com
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>