zynq: sdhci: Define max clock by macro

zc1571 with silicon can operate on 200MHz maximum frequency. Setup this
frequency by default and fix setting for ep108.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
diff --git a/include/configs/zynq-common.h b/include/configs/zynq-common.h
index f33a3bc..d10f1dd 100644
--- a/include/configs/zynq-common.h
+++ b/include/configs/zynq-common.h
@@ -105,6 +105,7 @@
 # define CONFIG_SDHCI
 # define CONFIG_ZYNQ_SDHCI
 # define CONFIG_CMD_MMC
+# define CONFIG_ZYNQ_SDHCI_MAX_FREQ	52000000
 #endif
 
 #ifdef CONFIG_ZYNQ_USB