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/k2l_evm_defconfig b/configs/k2l_evm_defconfig
index 6ecb409..1b21ed0 100644
--- a/configs/k2l_evm_defconfig
+++ b/configs/k2l_evm_defconfig
@@ -11,4 +11,5 @@
 CONFIG_OF_CONTROL=y
 CONFIG_DM=y
 CONFIG_SPI_FLASH=y
+CONFIG_SPI_FLASH_STMICRO=y
 CONFIG_SYS_NS16550=y