CFE_PSP_WatchdogInit method is not present in ut_psp_stub.c file

[asgibson]

Describe the bug
Receiving an error during building unit tests that states "undefined reference to `CFE_PSP_WatchdogInit' " while testing a method that calls the CFE_PSP_WatchdogInit method.

To Reproduce
Steps to reproduce the behavior:

1. Find a production code method that uses the CFE_PSP_WatchdogInit
2. Write a unit test that tests that function
3. Attempt to build
4. See error

Expected behavior
Build successfully, run tests with them able to use the stubbed behavior from CFE_PSP_WatchdogInit.

Code snips
The production code declaration:

PSP/fsw/inc/cfe_psp.h

Lines 330 to 333 in 1bd7bd9

	extern void CFE_PSP_WatchdogInit(void);
	/*
	** CFE_PSP_WatchdogInit configures the watchdog timer.
	*/

System observed on:

• Hardware: Dell Precision 7730
• OS: RHEL 8.6
• Versions: tag v1.6.0-rc4, also main branch

Additional context
This is only one of many watchdog methods in PSP; none are present in the ut_psp_stubs.c file. I did not encounter the usage of any other of these watchdog methods, yet.

Reporter Info
Alan Gibson
NASA/GSFC Code 587

[skliper]

Related to #284