lib: sbi: alloc tlb fifo by sbi_malloc

If the system is defined from tlb_fifo_num_entries, the scratch may be
too small to hold the fifo, so it is alloc through the heap.

Signed-off-by: Xiang W <wxjstz@126.com>
Signed-off-by: Xing Xiaoguang <xiaoguang.xing@sophgo.com>
Reviewed-by: Anup Patel <anup@brainfault.org>