drm/ttm: add TTM_PL_FLAG_CONTIGUOUS v2

This allows drivers to specify if they need a contiguous allocation or not.

v2: use space instead of tab

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Nicolai Hähnle <nicolai.haehnle@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>