arm64: zynqmp: Do not call bss init and board_init_r from board_init_f

There is no reason to clear bss and call board_init_r() from board_init_f()
beca it can be called directly from crt0_64.S with also support for SPL
stack relocation to SDRAM.
For more information please take a look at arch/arm/lib/crt0_64.S

Signed-off-by: Michal Simek <michal.simek@xilinx.com>