drm_hwcomposer: Move importer.h to platform.h

We're going to need more platform-specific stuff, so lump it
all in the same header.

BUG=b/28117135
TEST=compiles

Change-Id: Idfe82e9a29a0bcd284a02b2e58af0e620fdc542b
Signed-off-by: Sean Paul <seanpaul@chromium.org>
9 files changed