defconfig: am437x_sk_evm: enable spi driver model

enable spi driver model for am437x_sk_evm as ti_qspi supports
driver model

Signed-off-by: Mugunthan V N <mugunthanvnm@ti.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Jagan Teki <jteki@openedev.com>

configs/am437x_sk_evm_defconfig

@@ -18,3 +18,6 @@ CONFIG_SPI_FLASH=y
 CONFIG_SPI_FLASH_MACRONIX=y
 CONFIG_SYS_NS16550=y
 CONFIG_TI_QSPI=y
+CONFIG_DM_SPI=y
+CONFIG_DM_SPI_FLASH=y
+CONFIG_SPI_FLASH_BAR=y