Every ARCH_CORTEX_A5x config selects ARCH_ARMV8A, and both
Toolchain.defs and cmake/Toolchain.cmake test CONFIG_ARCH_ARMV8A at
the head of the chain, so the -mcpu=cortex-a53/a55/a57/a72 branches
were unreachable and all Cortex-A targets built with plain
-march=armv8-a, losing per-core scheduling/tuning.
Test the specific cores first so -mcpu wins for them; the generic
ARCH_ARMV8A branch still covers cores without a dedicated entry and
keeps the armv8.5-a/MTE handling. Also add the missing cortex-a55
branch to the cmake toolchain for parity with the makefile.
Signed-off-by: rikaken2004 <244897142+rikaken2004@users.noreply.github.com>