mx6: Select MX6QDL option via Kconfig

Currently the MX6QDL option is selected via CONFIG_SYS_EXTRA_OPTIONS,
but it is better to select it directly via Kconfig.

Signed-off-by: Fabio Estevam <fabio.estevam@nxp.com>
diff --git a/configs/pfla02_defconfig b/configs/pfla02_defconfig
index 456ae65..029c9de 100644
--- a/configs/pfla02_defconfig
+++ b/configs/pfla02_defconfig
@@ -12,7 +12,7 @@
 CONFIG_SPL_WATCHDOG_SUPPORT=y
 CONFIG_CMD_HDMIDETECT=y
 CONFIG_FIT=y
-CONFIG_SYS_EXTRA_OPTIONS="IMX_CONFIG=arch/arm/mach-imx/spl_sd.cfg,MX6QDL"
+CONFIG_SYS_EXTRA_OPTIONS="IMX_CONFIG=arch/arm/mach-imx/spl_sd.cfg"
 CONFIG_BOOTDELAY=3
 CONFIG_BOARD_EARLY_INIT_F=y
 CONFIG_SPL=y