microblaze: spl: Do not call mem_malloc_init and use early alloc
This patch has some parts connected together:
- Use _gd in bss section which is automatically cleared
Location at SPL_MALLOC_END wasn't cleared at all
- Use MALLOC_F_LEN(early alloc) instead of FULL MALLOC
(mem_malloc_init is not called at all)
- Simplify malloc and stack init.
At the end of SPL addr is malloc area and below is stack
Signed-off-by: Michal Simek <michal.simek@xilinx.com>