Increase BUFFERSIZE for POWER8-10 and use same value for POWER6

to fix overflow warning for PWR8 ZGEMM and PWR9 C/ZGEMM and avoid size mismatches in DYNAMIC_ARCH

common_power.h

@@ -844,8 +844,8 @@ Lmcount$lazy_ptr:
 #define BUFFER_SIZE     (  2 << 20)
 #elif defined(PPC440FP2)
 #define BUFFER_SIZE     ( 16 << 20)
-#elif defined(POWER8) || defined(POWER9) || defined(POWER10)
-#define BUFFER_SIZE     ( 64 << 20)
+#elif defined(POWER6) || defined(POWER8) || defined(POWER9) || defined(POWER10)
+#define BUFFER_SIZE     ( 32 << 22)
 #else
 #define BUFFER_SIZE     ( 16 << 20)
 #endif