reset: minimize the number of headers included from <linux/reset.h>

Commit 62e24c57 ("reset: add exported __reset_control_get, return
NULL if optional") moved the dev->of_node reference to core.c, so
<linux/reset.h> does not need to know the members of struct device.
Declaring device and device_node as structure is enough.

<linux/types.h> is necessary for bool, true, and false.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>