pinctrl: move pinctrl-maps debugfs file to top-level

The debugfs file pinctrl-maps is a system-wide file, not specific to any
pin controller, so place it in the top-level directory.

Also, move the code implementing the file to keep the order of all the
functions matching the order they're created in pinctrl_init_*debugfs().
The only non-obvious change here is no private data is passed to
debugfs_create_file() or single_open().

Signed-off-by: Stephen Warren <swarren@nvidia.com>
Acked-by: Dong Aisheng <dong.aisheng@linaro.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>