tools/testing/memblock: fix stale NUMA reservation tests

tools/testing/memblock: fix stale NUMA reservation tests

memblock allocations now reserve memory with MEMBLOCK_RSRV_KERN and,
on NUMA configurations, record the requested node on the reserved
region. Several memblock simulator NUMA tests still expected merges
that only worked before those reservation semantics changed, so the
suite aborted even though the allocator behavior was correct.

Update the NUMA merge expectations in the memblock_alloc_try_nid()
and memblock_alloc_exact_nid_raw() tests to match the current reserved
region metadata rules. For cases that should still merge, create the
pre-existing reservation with matching nid and MEMBLOCK_RSRV_KERN
metadata. Also strengthen the memblock_alloc_node() coverage by
checking the newly created reserved region directly instead of
re-reading the source memory node descriptor.

Finally, drop the stale README/TODO notes that still claimed
memblock_alloc_node() could not be tested.

The memblock simulator passes again with NUMA enabled after these
updates.

Signed-off-by: Priyanshu Kumar <priyanshukumarpu@gmail.com>
Link: https://patch.msgid.link/20260415122731.1768912-1-priyanshukumarpu@gmail.com
[rppt: dropped unrelated changes]
Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>