arm: socfpga: Fix FPGA bitstream programming routine

In case the FPGA bitstream is aligned to 4 bytes, skip the
part of the assembler which handles unaligned bitstream.
Otherwise, that part will loop indefinitelly.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Dinh Nguyen <dinguyen@opensource.altera.com>