mmc: zynq_sdhci: Use set_control_reg from sdhci.c

Since set_control_reg is available in sdhci.c, use it and remove
arasan_sdhci_set_control_reg().

Signed-off-by: Ashok Reddy Soma <ashok.reddy.soma@xilinx.com>
Reviewed-by: Jaehoon Chung <jh80.chung@samsung.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>