rockchip: rk3399: update defconfig for TPL

The SPL is now running at SDRAM, and 0x10000 is used by BL31,
and the ARM SPL do not support relocate now, we need reserved
0x50000 so that it won't overwrite the code when we load the
bl31 to target space.
We should remove this after we enable the relocate feature.

The SPL need malloc 0x9000 for MMC as buffer used for transfer
data to IRAM(The EMMC DMA can not transfer data to IRAM directly).

Signed-off-by: Kever Yang <kever.yang@rock-chips.com>