rockchip/rk3399: Cleanup platform.mk file
rockchip/rk3399: Cleanup platform.mk file

This makes the file consistently use tabs instead of mixing in spaces.

Signed-off-by: Derek Basehore <fb1ef5d447d8cd53e9e4511d7b18b7cdbb10397f@chromium.org>

lsigithub/arm-trusted-firmware_public,achingupta/arm-trusted-firmware,lsigithub/arm-trusted-firmware_public,achingupta/arm-trusted-firmware,sbranden/arm-trusted-firmware,sbranden/arm-trusted-firmware