KVM: nSVM: rename nested_load_control_from_vmcb12 in nested_copy_vmcb_control_to_cache

Following the same naming convention of the previous patch,
rename nested_load_control_from_vmcb12.
In addition, inline copy_vmcb_control_area as it is only called
by this function.

__nested_copy_vmcb_control_to_cache() works with vmcb_control_area
parameters and it will be useful in next patches, when we use
local variables instead of svm cached state.

Signed-off-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
Message-Id: <20211103140527.752797-4-eesposit@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>