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/configs/xilinx_zynqmp_ep_defconfig b/configs/xilinx_zynqmp_ep_defconfig
index 7f8e774..00db5e3 100644
--- a/configs/xilinx_zynqmp_ep_defconfig
+++ b/configs/xilinx_zynqmp_ep_defconfig
@@ -3,6 +3,7 @@
 CONFIG_ARCH_ZYNQMP=y
 CONFIG_SYS_TEXT_BASE=0x8000000
 CONFIG_SYS_MALLOC_F_LEN=0x8000
+CONFIG_ZYNQ_SDHCI_MAX_FREQ=52000000
 CONFIG_ZYNQMP_USB=y
 CONFIG_DEFAULT_DEVICE_TREE="zynqmp-ep108"
 CONFIG_DEBUG_UART=y