Build: Add stub functions of system calls

GNU Arm compiler version greater equal than *11.3.Rel1*
has a linker issue that required system calls are missing,
such as _read and _write. Add stub functions of required
system calls to solve this issue.

Signed-off-by: Chendi Sun <chendi.sun@arm.com>
Change-Id: I1384a405174097639e4c7bb71f19d01a66318a2d
6 files changed