arm64: zynqmp: Do not use SPL_SYS_MALLOC_SIMPLE allocator

arm64: zynqmp: Do not use SPL_SYS_MALLOC_SIMPLE allocator

This was caused by: "fs/fat: Reduce stack usage"
 (sha1:2460098cffacd18729262e3ed36656e6943783ed) which converted
fat code to use malloc. But simple malloc is not freeing space
that's why full malloc implementation is needed.
Malloc space is added to RAM.

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