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/zc5601_defconfig b/configs/zc5601_defconfig
index ca851f1..3f57d58 100644
--- a/configs/zc5601_defconfig
+++ b/configs/zc5601_defconfig
@@ -20,6 +20,7 @@
 CONFIG_BOARD_EARLY_INIT_F=y
 CONFIG_SPL_EXT_SUPPORT=y
 CONFIG_SPL_I2C_SUPPORT=y
+CONFIG_CMD_MEMTEST=y
 CONFIG_CMD_GPIO=y
 CONFIG_CMD_I2C=y
 CONFIG_CMD_MMC=y