hikey960: fix memory overlapped in memory map

MAP_TSP_MEM could be either in SRAM or DRAM. When MAP_TSP_MEM is in
DRAM, it's overlapped with MAP_DDR.

Since TSP_MEM is always configured in DRAM case, it means
MAP_OPTEE_PAGEABLE is always disabled. Just remove it.

Signed-off-by: Haojian Zhuang <haojian.zhuang@linaro.org>