multi-arch.yml and linuxkm.yml were installing apt packages with inline
shell commands. Replace them with the install-apt-deps composite action
for consistent retry behavior and caching.
* rename can_save_vector_registers_x86(), save_vector_registers_x86(), and restore_vector_registers_x86(), with wc_ prefix, and properly export them;
* move setup for WOLFSSL_LINUXKM_USE_SAVE_VECTOR_REGISTERS outside BUILDING_WOLFSSL gate;
* fix !BUILDING_WOLFSSL bindings for DISABLE_VECTOR_REGISTERS() to properly fall through to no-ops in !WOLFSSL_LINUXKM_USE_SAVE_VECTOR_REGISTERS configs, and properly #error if WOLFSSL_LINUXKM_USE_SAVE_VECTOR_REGISTERS but !CONFIG_X86;
.github/workflows/linuxkm.yml: --enable-linuxkm-benchmarks for additional coverage.