gpu/tests/gpu_buddy: Add gpu_test_buddy_alloc_range for exact-range allocation

gpu/tests/gpu_buddy: Add gpu_test_buddy_alloc_range for exact-range allocation

Add a new kunit test gpu_test_buddy_alloc_range() that exercises the
__gpu_buddy_alloc_range() exact-range allocation path, triggered when
start + size == end with flags=0.

The test covers:
- Basic exact-range allocation of the full mm
- Exact-range allocation of equal sub-ranges (quarters)
- Minimum chunk-size exact ranges at start, middle, and end offsets
- Non power-of-two mm size with multiple roots, including cross-root
  exact-range allocation
- Randomized exact-range allocations of N contiguous page-aligned
  slices in random order
- Negative: partially allocated range must reject overlapping exact
  alloc
- Negative: checkerboard allocation pattern rejects exact range over
  partially occupied pairs
- Negative: misaligned start, unaligned size, and out-of-bounds end
- Free and re-allocate the same exact range across multiple iterations
- Various power-of-two exact ranges at natural alignment

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/20260302150947.47535-2-sanjay.kumar.yadav@intel.com