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/ls1088ardb_qspi_defconfig b/configs/ls1088ardb_qspi_defconfig
index d568156..d4d2e42 100644
--- a/configs/ls1088ardb_qspi_defconfig
+++ b/configs/ls1088ardb_qspi_defconfig
@@ -12,6 +12,7 @@
 CONFIG_SYS_EXTRA_OPTIONS="SYS_FSL_DDR4, QSPI_BOOT"
 # CONFIG_USE_BOOTCOMMAND is not set
 # CONFIG_DISPLAY_BOARDINFO is not set
+CONFIG_CMD_MEMTEST=y
 CONFIG_CMD_I2C=y
 CONFIG_CMD_MMC=y
 CONFIG_CMD_SF=y