ppc: Generalize the kvmppc_get_clockfreq() function

ppc: Generalize the kvmppc_get_clockfreq() function

Currently the kvmppc_get_clockfreq() function reads the host's clock
frequency from /proc/device-tree, which is useful to past to the guest
in KVM setups.  However, there are some other host properties
advertised in the device tree which can also be relevant to the
guests.

This patch, therefore, replaces kvmppc_get_clockfreq() which can
retrieve any named, single integer property from the host device
tree's CPU node.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Alexander Graf <agraf@suse.de>