Relocate the OT platform file to the correct dir

Change-Id: I060fdd69c4158cc16aa08cff3b5505d7e600820f
diff --git a/opentitan-earlgrey-gen.repl b/platforms/opentitan-earlgrey-gen.repl
similarity index 100%
rename from opentitan-earlgrey-gen.repl
rename to platforms/opentitan-earlgrey-gen.repl