mmc: Added Kconfig support for CONFIG_ZYNQ_SDHCI_MAX_FREQ

This patch added Kconfig support for CONFIG_ZYNQ_SDHCI_MAX_FREQ
and enabled it in respective defconfig.

Signed-off-by: Vipul Kumar <vipulk@xilinx.com>
Signed-off-by: Siva Durga Prasad Paladugu <sivadur@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>
diff --git a/arch/arm/mach-zynq/Kconfig b/arch/arm/mach-zynq/Kconfig
index b9cd45b..8772904 100644
--- a/arch/arm/mach-zynq/Kconfig
+++ b/arch/arm/mach-zynq/Kconfig
@@ -63,4 +63,7 @@
 	  Add register writes to boot.bin format (max 256 pairs).
 	  Expect a table of register-value pairs, e.g. "0x12345678 0x4321"
 
+config ZYNQ_SDHCI_MAX_FREQ
+	default 52000000
+
 endif