MIPS: malta: malta-memory: Add free_init_pages_eva() callback

Use a Malta specific function to free the init section once the
kernel has booted. When operating in EVA mode, the physical memory
is shifted to 0x80000000. Kernel is loaded into 0x80000000 (virtual)
so the offset between physical and virtual addresses is 0.

Signed-off-by: Markos Chandras <markos.chandras@imgtec.com>