drm/tests/drm_buddy: Add tests for allocations exceeding max_order

drm/tests/drm_buddy: Add tests for allocations exceeding max_order

Add kunit tests that exercise edge cases where allocation requests
exceed mm->max_order after rounding. This can happen with
non-power-of-two VRAM sizes when the allocator rounds up requests.

For example, with 10G VRAM (8G + 2G roots), mm->max_order represents
the 8G block. A 9G allocation can round up to 16G in multiple ways:
CONTIGUOUS allocation rounds to next power-of-two, or non-CONTIGUOUS
with 8G min_block_size rounds to next alignment boundary.

The test validates CONTIGUOUS and RANGE flag combinations, ensuring that
only CONTIGUOUS-alone allocations use try_harder fallback, while other
combinations return -EINVAL when rounded size exceeds memory, preventing
BUG_ON assertions.

Cc: Christian König <christian.koenig@amd.com>
Cc: Arunpravin Paneer Selvam <Arunpravin.PaneerSelvam@amd.com>
Suggested-by: Matthew Auld <matthew.auld@intel.com>
Signed-off-by: Sanjay Yadav <sanjay.kumar.yadav@intel.com>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Signed-off-by: Arunpravin Paneer Selvam <Arunpravin.PaneerSelvam@amd.com>
Link: https://patch.msgid.link/20260108113227.2101872-6-sanjay.kumar.yadav@intel.com