[Draft proposal, subject to discussions]
Abstract assembly instructions to -
arch/interrupt.S (architecture specific assembly code for interrupt handling)
arch/svc.S (arch specific svc handling)
arch/mpu.c (weak functions that implement Arm MPUs, can be overridden by platform)
arch/tz.c/s - weak binding to veneer functions (only for v8m) that can be overridden by platform implementation.