mmc2 has a special pin for eMMC hardware reset, which is controllable
from the controller. Add the "mmc-cap-hw-reset" property to denote that
this controller supports this function, and the pins are actually used.

Also increase the signal drive strength for mmc2 pins, for HS-DDR mode
support.
Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>