drm/amdkfd: Unify gfx9/gfx10 context save area layouts

Add some padding before the MODE register in the HWREGs block to
preserve the same layout as gfx9. This simplifies implementation of a
user-mode debugger.

Signed-off-by: Laurent Morichetti <laurent.morichetti@amd.com>
Reviewed-by: Jay Cornwall <jay.cornwall@amd.com>
Acked-by: Felix Kuehling <Felix.Kuehling@amd.com>
Signed-off-by: Felix Kuehling <Felix.Kuehling@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>