rockchip: rk3399-puma: Update SPL_PAD_TO Kconfig option

On rk3399-puma the FIT payload is located at sector 0x200 compared
to the more Rockchip common sector 0x4000 offset:

  SYS_MMCSD_RAW_MODE_U_BOOT_SECTOR=0x200

Because FIT payload is located at sector 0x200 and IDBlock is located at
sector 64, the combined size of TPL+SPL (idbloader.img) cannot take up
more than 224 KiB:

  (0x200 - 64) x 512 = 0x38000 (224 KiB)

Adjust SPL_PAD_TO to match the used 0x200 sector offset.

Signed-off-by: Jonas Karlman <jonas@kwiboo.se>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>