threadx: Adding mutex control code implementation

Adding mutex control code implementation for THREADX
in which these functions would be used by libc inside
the printf function to prevent race conditions which results
in corrupted statements on the serial terminal. These functions
are already implemented by RTX, and FREERTOS and that's why
this issue is only seen in case of THREADX RTOS with ARMClang
compiler. In case of GCC compiler these functions are implemented
in gcc_retarget.c file so the issue is not seen in case of GCC too.

Signed-off-by: Ahmed.Ismail <Ahmed.Ismail@arm.com>