powerpc/powernv: Skip registering log region when CONFIG_PRINTK=n
powerpc/powernv: Skip registering log region when CONFIG_PRINTK=n

When CONFIG_PRINTK=n, log_buf_addr_get() returns NULL and log_buf_len_get()
return 0. Check for these return values and skip registering the dump buffer.

Signed-off-by: Pranith Kumar <99f39d96f0d0b011d351b608fe7e2870596fa4a9@gmail.com>
Reviewed-by: Stewart Smith <ec31ab75ddf977353c8f660f92ea8b23f64aef25@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <864f124608374e06e4da1fa5d2e47ed839b95411@ellerman.id.au>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs