aspeed: Reset Driver

Add Reset Driver for ast2500 SoC. This driver uses Watchdog Timer to
perform resets and thus depends on it. The actual Watchdog device used
needs to be configured in Device Tree using "aspeed,wdt" property, which
must be WDT phandle, for example:

rst: reset-controller {
    compatible = "aspeed,ast2500-reset";
    aspeed,wdt = <&wdt1>;
}

Signed-off-by: Maxim Sloyko <maxims@google.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/reset/Makefile b/drivers/reset/Makefile
index 2b96396..630b4b4 100644
--- a/drivers/reset/Makefile
+++ b/drivers/reset/Makefile
@@ -9,3 +9,4 @@
 obj-$(CONFIG_TEGRA_CAR_RESET) += tegra-car-reset.o
 obj-$(CONFIG_TEGRA186_RESET) += tegra186-reset.o
 obj-$(CONFIG_RESET_UNIPHIER) += reset-uniphier.o
+obj-$(CONFIG_AST2500_RESET) += ast2500-reset.o