ARM: at91: mmc portA support is only for at91sam9g20ek_2mmc board

Current the MMC support will enable MCI port A, Which is only exist
for 2mmc board.
So by default we need to disable MMC (port A) support. And only enable
it for 2mmc board. Otherwise, dataflash won't work in at91sam9260ek board
as MMC has confliction with Dataflash in the CLK pin.

Signed-off-by: Josh Wu <josh.wu@atmel.com>

configs/at91sam9g20ek_2mmc_defconfig

@@ -0,0 +1,3 @@
+CONFIG_SYS_EXTRA_OPTIONS="AT91SAM9G20,AT91SAM9G20EK_2MMC,SYS_USE_MMC"
+CONFIG_ARM=y
+CONFIG_TARGET_AT91SAM9260EK=y

configs/at91sam9g20ek_mmc_defconfig

@@ -1,3 +0,0 @@
-CONFIG_SYS_EXTRA_OPTIONS="AT91SAM9G20,SYS_USE_MMC"
-CONFIG_ARM=y
-CONFIG_TARGET_AT91SAM9260EK=y

include/configs/at91sam9260ek.h

@@ -90,7 +90,6 @@
 #define CONFIG_CMD_PING		1
 #define CONFIG_CMD_DHCP		1
 #define CONFIG_CMD_NAND		1
-#define CONFIG_CMD_MMC
 #define CONFIG_CMD_FAT
 #define CONFIG_CMD_USB		1
 
@@ -133,14 +132,17 @@
 # define CONFIG_MACH_TYPE MACH_TYPE_AT91SAM9260EK
 #endif
 
-/* DataFlash */
 #ifndef CONFIG_AT91SAM9G20EK_2MMC
+/* DataFlash */
 #define CONFIG_ATMEL_DATAFLASH_SPI
 #define CONFIG_HAS_DATAFLASH		1
 #define CONFIG_SYS_MAX_DATAFLASH_BANKS		2
 #define CONFIG_SYS_DATAFLASH_LOGIC_ADDR_CS0	0xC0000000	/* CS0 */
 #define CONFIG_SYS_DATAFLASH_LOGIC_ADDR_CS1	0xD0000000	/* CS1 */
 #define AT91_SPI_CLK			15000000
+#else
+/* Enable MMC. The MCCK is conflicted with DataFlash */
+#define CONFIG_CMD_MMC
 #endif
 
 #ifdef CONFIG_AT91SAM9G20EK