arm64: zynqmp: Fix emmc boot mode boot_target sequence

Emmc boot devcie is mounted to mmc@ff160000 controller on zynqmp.
Detect mmc alias at run time for setting up proper boot_targets
sequence instead of setting boot_targets manually.
Removed setting "modeboot" variable as it not longer need as we
switched to distro boot.

Signed-off-by: T Karthik Reddy <t.karthik.reddy@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>
1 file changed