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/strider_con_dp_defconfig b/configs/strider_con_dp_defconfig
index 129635d..5b5c3d1 100644
--- a/configs/strider_con_dp_defconfig
+++ b/configs/strider_con_dp_defconfig
@@ -18,6 +18,7 @@
 CONFIG_AUTOBOOT_STOP_STR=" "
 CONFIG_CMD_IMLS=y
 CONFIG_CMD_MEMTEST=y
+CONFIG_SYS_ALT_MEMTEST=y
 CONFIG_CMD_FPGAD=y
 CONFIG_CMD_I2C=y
 CONFIG_CMD_MMC=y