zynq-common: increase malloc pool len by dfu mmc file buffer size

The dfu mmc file buffer, which was static, now is allocated
by memalign(), so the malloc pool len should be also increased.

Signed-off-by: Przemyslaw Marczak <p.marczak@samsung.com>
Cc: Jagannadha Sutradharudu Teki <jaganna@xilinx.com>
Cc: Michal Simek <monstr@monstr.eu>
Acked-by: Michal Simek <michal.simek@xilinx.com>