test_overflow: Regularize test reporting output

Report test run summaries more regularly, so it's easier to understand
the output:
- Remove noisy "ok" reports for shift and allocator tests.
- Reorganize per-type output to the end of each type's tests.
- Replace redundant vmalloc tests with __vmalloc so that __GFP_NO_WARN
  can be used to keep the expected failure warnings out of dmesg,
  similar to commit 8e060c21 ("lib/test_overflow.c: avoid tainting
  the kernel and fix wrap size")

Resulting output:

  test_overflow: 18 u8 arithmetic tests finished
  test_overflow: 19 s8 arithmetic tests finished
  test_overflow: 17 u16 arithmetic tests finished
  test_overflow: 17 s16 arithmetic tests finished
  test_overflow: 17 u32 arithmetic tests finished
  test_overflow: 17 s32 arithmetic tests finished
  test_overflow: 17 u64 arithmetic tests finished
  test_overflow: 21 s64 arithmetic tests finished
  test_overflow: 113 shift tests finished
  test_overflow: 17 overflow size helper tests finished
  test_overflow: 11 allocation overflow tests finished
  test_overflow: all tests passed

Acked-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Link: https://lore.kernel.org/all/eb6d02ae-e2ed-e7bd-c700-8a6d004d84ce@rasmusvillemoes.dk/


Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Link: https://lore.kernel.org/all/CAKwvOdnYYa+72VhtJ4ug=SJVFn7w+n7Th+hKYE87BRDt4hvqOg@mail.gmail.com/


Signed-off-by: Kees Cook <keescook@chromium.org>