ARM: zynq: Align bss and end of u-boot image to 64bits

The main reason is that DT memory reserved code is expecting DT to be 64bit
aligned. For more information take a look at commit 5bd5ee02 ("xilinx:
zynqmp: Check that DT is 64bit aligned").

Signed-off-by: Michal Simek <michal.simek@amd.com>
Link: https://lore.kernel.org/r/9f3688cda188d8ea0b462df2aa08a10ddcc9c149.1661938136.git.michal.simek@amd.com