We want to be able to call virt data exchange conditionally
after gmc sw init to reserve bad pages as early as possible.
Since this is a conditional call, we will need
to call it again unconditionally later in the init sequence.

Refactor the data exchange function so it can be
called multiple times without re-initializing the work item.

v2: Cleaned up the code. Kept the original call to init_exchange_data()
inside early init to initialize the work item, afterwards call
exchange_data() when needed.
Signed-off-by: Victor Skvortsov <victor.skvortsov@amd.com>
Reviewed By: Shaoyun.liu <Shaoyun.liu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>