ARM: imx6: dh-imx6: Drop the SF hunk in config

There is now CONFIG_SPL_DM_SPI{,_FLASH}, however keeping
CONFIG_DM_SPI{,_FLASH} enabled in SPL seems to grow the SPL
by a couple of bytes:
      text    data     bss     dec     hex filename
 -   34069    1568      96   35733    8b95 spl/u-boot-spl
 +   34075    1568      96   35739    8b9b spl/u-boot-spl
In either case, the binary is bootable, so remove the part
in board config.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Andreas Geisreiter <ageisreiter@dh-electronics.de>
Cc: Jagan Teki <jagan@amarulasolutions.com>
Cc: Ludwig Zenz <lzenz@dh-electronics.de>
Cc: Stefano Babic <sbabic@denx.de>
Cc: Tom Rini <trini@konsulko.com>
diff --git a/include/configs/dh_imx6.h b/include/configs/dh_imx6.h
index 008a70a..4a469af 100644
--- a/include/configs/dh_imx6.h
+++ b/include/configs/dh_imx6.h
@@ -52,12 +52,6 @@
 /* SATA Configs */
 #define CONFIG_LBA48
 
-/* SPI Flash Configs */
-#if defined(CONFIG_SPL_BUILD)
-#undef CONFIG_DM_SPI
-#undef CONFIG_DM_SPI_FLASH
-#endif
-
 /* UART */
 #define CONFIG_MXC_UART_BASE		UART1_BASE