powerpc/fadump: when fadump is supported register the fadump sysfs files.

Currently it is not possible to distinguish the case when fadump is
supported by firmware and disabled in kernel and completely unsupported
using the kernel sysfs interface. User can investigate the devicetree
but it is more reasonable to provide sysfs files in case we get some
fadumpv2 in the future.

With this patch sysfs files are available whenever fadump is supported
by firmware.

There is duplicate message about lack of support by firmware in
fadump_reserve_mem and setup_fadump. Remove the duplicate message in
setup_fadump.

Signed-off-by: Michal Suchanek <msuchanek@suse.de>
Reviewed-by: Hari Bathini <hbathini@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20191107164757.15140-1-msuchanek@suse.de