drm/amdgpu: add flags to emit_ib interface v2

Replace the last bool type parameter with a general flags parameter,
to make the last parameter be able to contain more information.

v2: drop setting need_ctx_switch = false

Reviewed-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Hawking Zhang <Hawking.Zhang@amd.com>
Signed-off-by: Jack Xiao <Jack.Xiao@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>