btrfs: simplify debug print helpers without enabled printk

The btrfs_debug() helpers depend on various config options. In case of
"no_printk" we don't need to define a special helper that in the end
does nothing but validates the parameters. As the default build config
is to validate the parameters we can simplify it to let the debug
helpers expand to nothing and remove btrfs_no_printk_in_rcu().

To avoid warnings use fs_info and inline one variable in
extent_from_logical().

Reviewed-by: Daniel Vacek <neelx@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>