Add a config option to enable debugfs support by default. And if debugfs
support is enabled by default, dump count default value is increased to 50
as generally users want something bigger than the current default in that
situation.

Link: https://lore.kernel.org/r/1611659068-131975-4-git-send-email-john.garry@huawei.comSigned-off-by: Luo Jiaxing <luojiaxing@huawei.com>
Signed-off-by: John Garry <john.garry@huawei.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>