spi: Move SPI drivers to defconfig

There are already Kconfig options for SPI 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/trimslice_defconfig b/configs/trimslice_defconfig
index 297353f..2b644d1 100644
--- a/configs/trimslice_defconfig
+++ b/configs/trimslice_defconfig
@@ -14,6 +14,7 @@
 # CONFIG_CMD_NFS is not set
 CONFIG_SPI_FLASH=y
 CONFIG_SYS_NS16550=y
+CONFIG_TEGRA20_SFLASH=y
 CONFIG_USB=y
 CONFIG_DM_USB=y
 CONFIG_USE_PRIVATE_LIBGCC=y