configs: j721e_evm_a72_defconfig: Enable MUX_MMIO at SPL

MUX_MMIO is required in SPL stage in order to boot hyperflash
successfully. Add configs to enable MUX_MMIO in SPL stage.

Signed-off-by: Anurag Dutta <a-dutta@ti.com>
diff --git a/configs/j721e_evm_a72_defconfig b/configs/j721e_evm_a72_defconfig
index 71e6c20..6bc7166 100644
--- a/configs/j721e_evm_a72_defconfig
+++ b/configs/j721e_evm_a72_defconfig
@@ -151,6 +151,7 @@
 CONFIG_SPI_FLASH_MTD=y
 CONFIG_MULTIPLEXER=y
 CONFIG_MUX_MMIO=y
+CONFIG_SPL_MUX_MMIO=y
 CONFIG_PHY_TI_DP83867=y
 CONFIG_PHY_FIXED=y
 CONFIG_TI_AM65_CPSW_NUSS=y