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/am335x_gp_evm_defconfig b/configs/am335x_gp_evm_defconfig
index b6c2198..74d9ffb 100644
--- a/configs/am335x_gp_evm_defconfig
+++ b/configs/am335x_gp_evm_defconfig
@@ -12,6 +12,7 @@
 CONFIG_OF_CONTROL=y
 CONFIG_DM_MMC=y
 CONFIG_SPI_FLASH=y
+CONFIG_SPI_FLASH_WINBOND=y
 CONFIG_DM_ETH=y
 CONFIG_SYS_NS16550=y
 CONFIG_RSA=y