tree dcd8a7d4ec57cfd4355dca9b059059e9974b8b3d
parent c37be00b160da5e8aa1a2950090fc52002d88d95
author Heyi Guo <heyi.guo@linaro.org> 1519901878 +0800
committer Heyi Guo <heyi.guo@linaro.org> 1520230684 +0800

Change PLATFORM_ROOT to TF_PLATFORM_ROOT

Since we use "?=" to set PLATFORM_ROOT, it is better to change the
name to be more special, or else it may be overridden by some
environment variables, such as in some CI build environments.

Signed-off-by: Heyi Guo <heyi.guo@linaro.org>