netfs: clean up after renaming FSCACHE_DEBUG config

netfs: clean up after renaming FSCACHE_DEBUG config

Commit 6b8e61472529 ("netfs: Rename CONFIG_FSCACHE_DEBUG to
CONFIG_NETFS_DEBUG") renames the config, but introduces two issues: First,
NETFS_DEBUG mistakenly depends on the non-existing config NETFS, whereas
the actual intended config is called NETFS_SUPPORT. Second, the config
renaming misses to adjust the documentation of the functionality of this
config.

Clean up those two points.

Signed-off-by: Lukas Bulwahn <lukas.bulwahn@redhat.com>
Link: https://lore.kernel.org/r/20240731073902.69262-1-lukas.bulwahn@redhat.com
Signed-off-by: Christian Brauner <brauner@kernel.org>