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/M54451EVB_stmicro_defconfig b/configs/M54451EVB_stmicro_defconfig
index 9b69415..21a2687 100644
--- a/configs/M54451EVB_stmicro_defconfig
+++ b/configs/M54451EVB_stmicro_defconfig
@@ -5,3 +5,4 @@
 # CONFIG_CMD_LOADS is not set
 # CONFIG_CMD_SETEXPR is not set
 CONFIG_SPI_FLASH=y
+CONFIG_SPI_FLASH_STMICRO=y