Convert CONFIG_SF_DEFAULT_* to Kconfig

This converts the following to Kconfig:
  CONFIG_SF_DEFAULT_BUS
  CONFIG_SF_DEFAULT_CS
  CONFIG_SF_DEFAULT_MODE
  CONFIG_SF_DEFAULT_SPEED

I use moveconfig script and then manual check on generated u-boot.cfg
to solve the remaining issue.

Signed-off-by: Patrick Delaunay <patrick.delaunay@st.com>
diff --git a/configs/x530_defconfig b/configs/x530_defconfig
index 25b9e88..cd18e9e 100644
--- a/configs/x530_defconfig
+++ b/configs/x530_defconfig
@@ -50,6 +50,8 @@
 CONFIG_NAND=y
 CONFIG_NAND_PXA3XX=y
 CONFIG_SPI_FLASH=y
+CONFIG_SF_DEFAULT_BUS=1
+CONFIG_SF_DEFAULT_SPEED=50000000
 CONFIG_SPI_FLASH_BAR=y
 CONFIG_SPI_FLASH_MACRONIX=y
 CONFIG_SPI_FLASH_STMICRO=y