Fix for CR-1219310 : Spatial sharing overhead test failure on linux

[aktondak]

Problem solved by the commit

This PR fixes CR-1219310

• The problem was identified as missing init_buffer call which made the instruction buffer have garbage value and causing the device to behave in-deterministically. It makes the test on Windows run as a no-op kernel but behave differently on linux

• This PR also cleans up some utility code in TestRunner class and correctly moves it to ValidateUtilities.

Bug / issue (if any) fixed, which PR introduced the bug, how it was discovered

CR-1219310
Discovered through testing on Linux by the Linux folks.

How problem was solved, alternative solutions (if any) and why they were rejected

The problem was solved through correctly using the df-bw control code and modifying the buffer sizes accordingly.

Risks (if any) associated the changes in the commit

N/A

What has been tested and how, request additional testing if necessary

Tested on Windows and linux platforms. Updated metric numbers after testing :
Windows :

Z:\Repos\XRT-MCDM-FORK\XRT-MCDM\build\WRelease\xilinx\xrt>xrt-smi validate --run spatial-sharing-overhead
Validate Device           : [00c5:00:01.1]
    Platform              : NPU
    Power Mode            : Performance
-------------------------------------------------------------------------------
Test 1 [00c5:00:01.1]     : spatial-sharing-overhead
    Details               : **Overhead: 654.9 ms**
    Test Status           : [PASSED]
Z:\Repos\XRT-MCDM-FORK\XRT-MCDM\build\WRelease\xilinx\xrt>xrt-smi validate --run temporal-sharing-overhead
Validate Device           : [00c5:00:01.1]
    Platform              : NPU
    Power Mode            : Performance
-------------------------------------------------------------------------------
Test 1 [00c5:00:01.1]     : temporal-sharing-overhead
    Details               : **Overhead: '682.7' ms**
    Test Status           : [PASSED]

Linux :

Test 8 [0000:c3:00.1]     : spatial-sharing-overhead                            
    Details               : Overhead: 2628.5 ms
    Test Status           : [PASSED]
-------------------------------------------------------------------------------
Test 9 [0000:c3:00.1]     : temporal-sharing-overhead                           
    Details               : Overhead: '2642.6' ms
    Test Status           : [PASSED]

Documentation impact (if any)

N\A

[gbuildx]

Can one of the admins verify this patch?