sf: Move SPI flash drivers to defconfig

There are already Kconfig options for SPI flash drivers, but we
have not moved them from config.h to defconfig files. This commit
does this in a batch.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
diff --git a/configs/B4860QDS_SRIO_PCIE_BOOT_defconfig b/configs/B4860QDS_SRIO_PCIE_BOOT_defconfig
index ae1356b..11db5bc 100644
--- a/configs/B4860QDS_SRIO_PCIE_BOOT_defconfig
+++ b/configs/B4860QDS_SRIO_PCIE_BOOT_defconfig
@@ -5,6 +5,7 @@
 # CONFIG_CMD_IMLS is not set
 # CONFIG_CMD_FLASH is not set
 CONFIG_SPI_FLASH=y
+CONFIG_SPI_FLASH_SST=y
 CONFIG_NETDEVICES=y
 CONFIG_E1000=y
 CONFIG_SYS_NS16550=y