kvm tools: provide a mechanism for translating host to guest addresses

When generating a device tree for a guest, it is useful to have a helper
for converting host addresses to guest addresses in order to populate
the device nodes correctly.

This patch adds such a helper, following a similar implementation to the
reverse translation function that already exists.

Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Pekka Enberg <penberg@kernel.org>