selftests/seccomp: Convert HAVE_GETREG into ARCH_GETREG/ARCH_SETREG

Instead of special-casing the get/set-registers routines, move the
HAVE_GETREG logic into the new ARCH_GETREG() and ARCH_SETREG() macros.

Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/lkml/20200912110820.597135-9-keescook@chromium.org


Acked-by: Christian Brauner <christian.brauner@ubuntu.com>