microblaze: Convert generic platform to DM gpio

Converting GPIO to DM requires to do changes in reset subsystem
that's why support for Microblaze soft reset via sysreset and GPIO
sysreset support was added.
These two patches enables enabling GPIO DM.
Microblaze soft reset is bind at last reset method.

GPIO reset is handled via sysreset with adding this fragment to DT.

gpio-restart {
	compatible = "gpio-restart";
	gpios = <&reset_gpio 0 0 0>;
	/* 3rd cell ACTIVE_HIGH = 0, ACTIVE_LOW = 1 */
};

hard-reset-gpio property is not documented and also handled.
Conversion is required.

Unfortunately do_reset is required for SPL that's why use only soft
microblaze reset for now.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>