Rename gyp file to highlight platform2 specifics

BUG=b:23764888
TEST=FEATURES=test emerge-gizmo libweave &&\
     cros_workon_make --board=gizmo libweave --test

Change-Id: If724108f5a33de38e3378dd651b4207d0272d253
diff --git a/libweave/libweave.gyp b/libweave/platform2.gyp
similarity index 100%
rename from libweave/libweave.gyp
rename to libweave/platform2.gyp