arm64: Remove tautological LLVM Kconfig conditions

arm64: Remove tautological LLVM Kconfig conditions

Now that the minimum supported version of LLVM for building the kernel
has been bumped to 15.0.0, two sets of always true conditions can be
safely removed in the arm64 Kconfig file.

Acked-by: Will Deacon <will@kernel.org>
Reviewed-by: Kees Cook <kees@kernel.org>
Link: https://lore.kernel.org/r/20250821-bump-min-llvm-ver-15-v2-4-635f3294e5f0@kernel.org
Signed-off-by: Nathan Chancellor <nathan@kernel.org>