ANDROID: KVM: arm64: Return a token for a pKVM module registration

Later introduction of custom HVCs will require to store some data.
Conviniently, the only thing we need is the start addr (in the hyp VA) of
the text section. So use this value as a token to avoid having to store
it anywhere.

Bug: 244543039
Bug: 244373730
Change-Id: Idd0bcbbb36d189aa4932833ca5b40382c2cddb08
Signed-off-by: Vincent Donnefort <vdonnefort@google.com>
Signed-off-by: Quentin Perret <qperret@google.com>