imx8mm_evk: Switch to new imx8mm evk board

Update PMIC to use PCA9540, the legacy board not supported by NXP

Signed-off-by: Ye Li <ye.li@nxp.com>
diff --git a/configs/imx8mm_evk_defconfig b/configs/imx8mm_evk_defconfig
index e22b7de..ae9e062 100644
--- a/configs/imx8mm_evk_defconfig
+++ b/configs/imx8mm_evk_defconfig
@@ -83,7 +83,7 @@
 CONFIG_SPL_PINCTRL=y
 CONFIG_PINCTRL_IMX8M=y
 CONFIG_DM_PMIC=y
-CONFIG_SPL_DM_PMIC_BD71837=y
+CONFIG_SPL_DM_PMIC_PCA9450=y
 CONFIG_DM_REGULATOR=y
 CONFIG_DM_REGULATOR_FIXED=y
 CONFIG_DM_REGULATOR_GPIO=y