SWDEV-323669 - Improve arch detection

- Clean up detection by using visual studio macros to detect arch; I
  didn't list all possible ARM platforms (can be done later if desired)
- Fixed two incorrect uses of !defined(ATI_ARCH_ARM) to instead use
  defined(ATI_ARCH_X86), as they contain X86 specific code
- Fixed one use of __ARM_ARCH_7A__ to use ATI_ARCH_ARM instead

This is an improvement to the fixes in the last patch for SWDEV-323669

Signed-off-by: Jeremy Newton <Jeremy.Newton@amd.com>
Change-Id: I8568167293c34ad5331902105877f3ab6e25acb3

rocclr/os/os.cpp

@@ -112,7 +112,7 @@ int Os::processorCount_ = 0;
 void Os::spinPause() {
 #if defined(ATI_ARCH_X86)
   _mm_pause();
-#elif defined(__ARM_ARCH_7A__)
+#elif defined(ATI_ARCH_ARM)
   __asm__ __volatile__("yield");
 #endif
 }