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/beaver_defconfig b/configs/beaver_defconfig
index 41e94e0..29f61c1 100644
--- a/configs/beaver_defconfig
+++ b/configs/beaver_defconfig
@@ -32,6 +32,8 @@
 CONFIG_DFU_SF=y
 CONFIG_SYS_I2C_TEGRA=y
 CONFIG_SPI_FLASH=y
+CONFIG_SF_DEFAULT_MODE=0
+CONFIG_SF_DEFAULT_SPEED=24000000
 CONFIG_SPI_FLASH_WINBOND=y
 CONFIG_RTL8169=y
 CONFIG_PCI=y