pico-pi-imx7d: Convert to watchdog driver model

Commit 68dcbdd594d4 ("ARM: imx: Add weak default reset_cpu()") caused
the 'reset' command in U-Boot to not cause a board reset.

Fix it by switching to the watchdog driver model via sysreset, which
is the preferred method for implementing the watchdog reset

Signed-off-by: Fabio Estevam <festevam@denx.de>
diff --git a/configs/pico-pi-imx7d_defconfig b/configs/pico-pi-imx7d_defconfig
index 48364c7..5b615da 100644
--- a/configs/pico-pi-imx7d_defconfig
+++ b/configs/pico-pi-imx7d_defconfig
@@ -76,6 +76,8 @@
 CONFIG_DM_PMIC_PFUZE100=y
 CONFIG_DM_SERIAL=y
 CONFIG_MXC_UART=y
+CONFIG_SYSRESET=y
+CONFIG_SYSRESET_WATCHDOG=y
 CONFIG_IMX_THERMAL=y
 CONFIG_USB=y
 CONFIG_SPL_USB_HOST=y
@@ -95,3 +97,4 @@
 CONFIG_SPLASH_SCREEN=y
 CONFIG_SPLASH_SCREEN_ALIGN=y
 CONFIG_BMP_16BPP=y
+CONFIG_IMX_WATCHDOG=y