KVM: arm64: Mark host bss and rodata section as shared

As the hypervisor maps the host's .bss and .rodata sections in its
stage-1, make sure to tag them as shared in hyp and host page-tables.

But since the hypervisor relies on the presence of these mappings, we
cannot let the host in complete control of the memory regions -- it
must not unshare or donate them to another entity for example. To
prevent this, let's transfer the ownership of those ranges to the
hypervisor itself, and share the pages back with the host.

Signed-off-by: Quentin Perret <qperret@google.com>
Reviewed-by: Fuad Tabba <tabba@google.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20210809152448.1810400-18-qperret@google.com