reset: sti: Remove STiH415/6 reset support

Support for STiH415/6 SoCs is being removed from the
kernel because the platforms are obsolete. This patch removes
the reset drivers for these SoC's.

Signed-off-by: Peter Griffin <peter.griffin@linaro.org>
Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>