reset: fix Kconfig menu to include reset drivers in sub-menu

reset: fix Kconfig menu to include reset drivers in sub-menu

In "make menuconfig", reset drivers are currently lined up together
with the reset sub-system menu, like this:

    -*- Reset Controller Support  ----
    < > Hi6220 Reset Driver

(It also means, the menu "Reset Controller Support" is always empty.)

"Hi6220 Reset Driver" should go into the sub-menu of the
"Reset Controller Support".

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