Build issues on AIX for POWER10 and POWER11 (microsoft#26704)

While building onnxruntime from source for AIX I ran into macro
pre-defined errors for the POWER10 and POWER11 machines. This patch
resolves the issue.

---------

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Author: KV2773

cmake/onnxruntime_mlas.cmake

@@ -636,9 +636,13 @@ else()
             enable_language(ASM)
             check_cxx_source_compiles("
               #ifdef _AIX
+              #include <sys/systemcfg.h>
+              #if !defined(POWER_10)
               #define POWER_10       0x40000
+              #endif
+              #if !defined(POWER_10_ANDUP)
               #define POWER_10_ANDUP (POWER_10)
-              #include <sys/systemcfg.h>
+              #endif
               #define __power_10_andup() (_system_configuration.implementation & POWER_10_ANDUP)
               int main() {
                 bool HasP10 = (__power_10_andup() && __power_mma_version() == MMA_V31);

onnxruntime/core/mlas/lib/platform.cpp

@@ -40,9 +40,13 @@ Module Name:
 #if defined(__linux__)
 #include <sys/auxv.h>
 #elif defined(_AIX)
+#include <sys/systemcfg.h>
+#if !defined(POWER_10)
 #define POWER_10       0x40000
+#endif
+#if !defined(POWER_10_ANDUP)
 #define POWER_10_ANDUP (POWER_10)
-#include <sys/systemcfg.h>
+#endif
 #define __power_10_andup() (_system_configuration.implementation & POWER_10_ANDUP)
 #elif defined(__FreeBSD__)
 #include <machine/cpu.h>