ARM: mx6: Disable PCIe on SABRE Lite/Nitrogen6x

Use of PCIe on SABRE Lite and Nitrogen6x boards
is atypical and requires the use of custom daughter
boards.

Use in U-Boot is even rarer, so this patch removes it from
the standard configuration.
Signed-off-by: NEric Nelson <eric.nelson@boundarydevices.com>
Acked-by: NMarek Vasut <marex@denx.de>

include/configs/nitrogen6x.h

@@ -355,7 +355,6 @@
 /*
  * PCI express
  */
-#define CONFIG_CMD_PCI
 #ifdef CONFIG_CMD_PCI
 #define CONFIG_PCI
 #define CONFIG_PCI_PNP