[POWERPC] Move of_device_get_modalias to drivers/of

Commit 140b932f ("Create modalias file
in sysfs for of_platform bus") needs this to avoid breaking the sparc
builds.

Just move the code and add whitespace around some binary operators.

Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
Acked-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Paul Mackerras <paulus@samba.org>