FROMLIST: alloc_tag: uninline code gated by mem_alloc_profiling_key in slab allocator

When a sizable code section is protected by a disabled static key, that
code gets into the instruction cache even though it's not executed and
consumes the cache, increasing cache misses. This can be remedied by
moving such code into a separate uninlined function.
On a Pixel6 phone, slab allocation profiling overhead measured with
CONFIG_MEM_ALLOC_PROFILING=y and profiling disabled is:

             baseline             modified
Big core     3.31%                0.17%
Medium core  3.79%                0.57%
Little core  6.68%                1.28%

This improvement comes at the expense of the configuration when profiling
gets enabled, since there is now an additional function call. The overhead
from this additional call on Pixel6 is:

Big core     0.66%
Middle core  1.23%
Little core  2.42%

However this is negligible when compared with the overall overhead of the
memory allocation profiling when it is enabled.
On x86 this patch does not make noticeable difference because the overhead
with mem_alloc_profiling_key disabled is much lower (under 1%) to start
with, so any improvement is less visible and hard to distinguish from the
noise. The overhead from additional call when profiling is enabled is also
within noise levels.

Link: https://lore.kernel.org/all/20250201231803.2661189-2-surenb@google.com/


Bug: 380948583
Change-Id: I9391cc1c034f98a83c23f27ba4739b219478adbc
Signed-off-by: Suren Baghdasaryan <surenb@google.com>