arm64: zynqmp: Split emmc configuration into emmc0 and emmc1

This patch splits the current mini emmc configuration into emmc0
and emmc1 configurations because emmc is probed at boot time and on
systems which have only one interface mini configuration is failing on
unused interface. This patch also adds required clock node in dts and
enables CONFIG_MMC_SDHCI_ZYNQ through defconfig.

Signed-off-by: Siva Durga Prasad Paladugu <siva.durga.paladugu@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>