Kconfig: Migrate CONFIG_CSF_SIZE to Kconfig

Move CONFIG_CSF_SIZE to Kconfig and define default value as 0x4000.

mx8mqevk requires 0x2000 add this configuration in imx8mq_evk_defconfig
file.

Signed-off-by: Breno Lima <breno.lima@nxp.com>
Reviewed-by: Fabio Estevam <festevam@gmail.com>
diff --git a/configs/imx8mq_evk_defconfig b/configs/imx8mq_evk_defconfig
index 59ba4bc..8d3cdec 100644
--- a/configs/imx8mq_evk_defconfig
+++ b/configs/imx8mq_evk_defconfig
@@ -7,6 +7,7 @@
 CONFIG_SPL_SERIAL_SUPPORT=y
 CONFIG_SPL=y
 CONFIG_SPL_TEXT_BASE=0x7E1000
+CONFIG_CSF_SIZE=0x2000
 CONFIG_FIT=y
 CONFIG_FIT_EXTERNAL_OFFSET=0x3000
 CONFIG_SPL_LOAD_FIT=y