powerpc/cacheinfo: Use name@unit instead of full DT path in debug messages

We know that every OF node we deal with in this code is under /cpus,
so we can make the debug messages a little less verbose without losing
information.

E.g.

cacheinfo: creating L1 dcache and icache for /cpus/PowerPC,POWER8@0
cacheinfo: creating L2 ucache for /cpus/l2-cache@2006
cacheinfo: creating L3 ucache for /cpus/l3-cache@3106

becomes

cacheinfo: creating L1 dcache and icache for PowerPC,POWER8@0
cacheinfo: creating L2 ucache for l2-cache@2006
cacheinfo: creating L3 ucache for l3-cache@3106

Replace all '%pOF' specifiers with '%pOFP'.

Signed-off-by: Nathan Lynch <nathanl@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20190627051537.7298-3-nathanl@linux.ibm.com