ARM: Clean up definition of ARM_HAS_GROUP_RELOCS

Now that the minimum supported version of LLVM for building the kernel
has been bumped to 15.0.0, the first depends line of
ARM_HAS_GROUP_RELOCS is always true, so it can be safely removed.
Combine the !COMPILE_TEST dependency into the 'def_bool' line and update
the comment as well.

Reviewed-by: Kees Cook <kees@kernel.org>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Link: https://lore.kernel.org/r/20250821-bump-min-llvm-ver-15-v2-3-635f3294e5f0@kernel.org


Signed-off-by: Nathan Chancellor <nathan@kernel.org>