Used the new gensyscalls.py script to update the ARM syscalls with the
BEGIN(x) and END(x) macros to give size information for the code of the
syscall. Useful for valgrind.
Change-Id: I8c481c8928401ac110fd19b087f7d67e4db39326
Only provide an implementation for ARM at the moment, since
it requires specific assembly fragments (the standard syscall
stubs cannot be used because the child returns in a different
stack).