treewide: mem: Enable MEMTEST via defconfig

There is no reason to enable MEMTEST from headers when was converted to
Kconfig already.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
diff --git a/configs/ls1012afrwy_tfa_defconfig b/configs/ls1012afrwy_tfa_defconfig
index 280dbd3..ca0575e 100644
--- a/configs/ls1012afrwy_tfa_defconfig
+++ b/configs/ls1012afrwy_tfa_defconfig
@@ -21,6 +21,7 @@
 # CONFIG_DISPLAY_BOARDINFO is not set
 CONFIG_DISPLAY_BOARDINFO_LATE=y
 CONFIG_CMD_GREPENV=y
+CONFIG_CMD_MEMTEST=y
 CONFIG_CMD_GPT=y
 CONFIG_CMD_I2C=y
 CONFIG_CMD_MMC=y