armv7: omap-common: make SPL board_mmc_init() weak

make this function weak, so board code can setup in SPL
MMC init with board special values.

Signed-off-by: Heiko Schocher <hs@denx.de>

arch/arm/cpu/armv7/omap-common/boot-common.c

@@ -200,7 +200,7 @@ void spl_board_init(void)
 #endif
 }
 
-int board_mmc_init(bd_t *bis)
+__weak int board_mmc_init(bd_t *bis)
 {
 	switch (spl_boot_device()) {
 	case BOOT_DEVICE_MMC1: