xen/arm: Rework the interface of p2m_lookup and use typesafe gfn and mfn

xen/arm: Rework the interface of p2m_lookup and use typesafe gfn and mfn

The prototype and the declaration of p2m_lookup disagree on how the
function should be used. One expect a frame number whilst the other
an address.

Thankfully, everyone is using with an address today. However, most of
the callers have to convert a guest frame to an address. Modify
the interface to take a guest physical frame in parameter and return
a machine frame.

Whilst modifying the interface, use typesafe gfn and mfn for clarity
and catching possible misusage.

Signed-off-by: Julien Grall <julien.grall@arm.com>
Acked-by: Stefano Stabellini <sstabellini@kernel.org>