lib/test_vmalloc.c: allow built-in execution

lib/test_vmalloc.c: allow built-in execution

Remove the dependency on module loading ("m") for the vmalloc test suite,
enabling it to be built directly into the kernel, so both ("=m") and
("=y") are supported.

Motivation:
- Faster debugging/testing of vmalloc code;
- It allows to configure the test via kernel-boot parameters.

Configuration example:
  test_vmalloc.nr_threads=64
  test_vmalloc.run_test_mask=7
  test_vmalloc.sequential_test_order=1

Link: https://lkml.kernel.org/r/20250417161216.88318-2-urezki@gmail.com
Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Reviewed-by: Baoquan He <bhe@redhat.com>
Reviewed-by: Adrian Huang <ahuang12@lenovo.com>
Tested-by: Adrian Huang <ahuang12@lenovo.com>
Cc: Christop Hellwig <hch@infradead.org>
Cc: Mateusz Guzik <mjguzik@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>