Convert CONFIG_QSPI_BOOT to Kconfig

This converts the following to Kconfig:
   CONFIG_QSPI_BOOT

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/ls1021aiot_qspi_defconfig b/configs/ls1021aiot_qspi_defconfig
index 5e2d725..2227113 100644
--- a/configs/ls1021aiot_qspi_defconfig
+++ b/configs/ls1021aiot_qspi_defconfig
@@ -12,7 +12,7 @@
 CONFIG_DEFAULT_DEVICE_TREE="ls1021a-iot-duart"
 CONFIG_AHCI=y
 CONFIG_SYS_LOAD_ADDR=0x82000000
-CONFIG_SYS_EXTRA_OPTIONS="QSPI_BOOT"
+CONFIG_QSPI_BOOT=y
 CONFIG_BOARD_EARLY_INIT_F=y
 CONFIG_MISC_INIT_R=y
 CONFIG_ID_EEPROM=y