treewide: Migrate CONFIG_SYS_ALT_MEMTEST to Kconfig

Migrate the CONFIG_SYS_ALT_MEMTEST option to Kconfig.

Signed-off-by: Mario Six <mario.six@gdsys.cc>
[trini: Re-run migration after also including CMD_MEMTEST]
Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/apalis_imx6_defconfig b/configs/apalis_imx6_defconfig
index 46492cf..623d28d 100644
--- a/configs/apalis_imx6_defconfig
+++ b/configs/apalis_imx6_defconfig
@@ -30,6 +30,7 @@
 CONFIG_CMD_ASKENV=y
 CONFIG_CRC32_VERIFY=y
 CONFIG_CMD_MEMTEST=y
+CONFIG_SYS_ALT_MEMTEST=y
 CONFIG_CMD_DFU=y
 CONFIG_CMD_GPIO=y
 CONFIG_CMD_I2C=y