edk2-platforms: Add License-History.txt

Add text file that contains the history of license and contributor
agreement changes.

https://bugzilla.tianocore.org/show_bug.cgi?id=1373

This change is based on the following emails:

  https://lists.01.org/pipermail/edk2-devel/2019-February/036260.html
  https://lists.01.org/pipermail/edk2-devel/2018-October/030385.html

RFCs with detailed process for the license change:

  V3: https://lists.01.org/pipermail/edk2-devel/2019-March/038116.html
  V2: https://lists.01.org/pipermail/edk2-devel/2019-March/037669.html
  V1: https://lists.01.org/pipermail/edk2-devel/2019-March/037500.html

Cc: Leif Lindholm <[email protected]>
Cc: Ard Biesheuvel <[email protected]>
Cc: Thad Gillispie <[email protected]>
Cc: Daocheng Bu <[email protected]>
Cc: Isaac W Oram <[email protected]>
Cc: Maciej Piwko <[email protected]>
Cc: Chasel Chiu <[email protected]>
Cc: Michael Kubacki <[email protected]>
Cc: Shifei A Lu <[email protected]>
Cc: Xiaohu Zhou <[email protected]>
Cc: Ankit Sinha <[email protected]>
Cc: Sai Chaganty <[email protected]>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Michael D Kinney <[email protected]>
Reviewed-by: Chasel Chiu <[email protected]>
Reviewed-by: Michael Kubacki <[email protected]>
Reviewed-by: Leif Lindholm <[email protected]>
Reviewed-by: Ankit Sinha <[email protected]>