ppc: do not pass redundant compiler flags

The -mpowerpc64 and -mpowerpc-gfxopt flags are implicitly set by
-mcpu as needed.  Passing them explicitly is redundant and can
conflict with user-supplied flags.
Signed-off-by: Mans Rullgard <mans@mansr.com>

configure

@@ -2505,20 +2505,20 @@ elif enabled ppc; then
             disable altivec
         ;;
         g3|75*|ppc75*|powerpc75*)
-            cpuflags="-mcpu=750 -mpowerpc-gfxopt"
+            cpuflags="-mcpu=750"
             disable altivec
         ;;
         g4|745*|ppc745*|powerpc745*)
-            cpuflags="-mcpu=7450 -mpowerpc-gfxopt"
+            cpuflags="-mcpu=7450"
         ;;
         74*|ppc74*|powerpc74*)
-            cpuflags="-mcpu=7400 -mpowerpc-gfxopt"
+            cpuflags="-mcpu=7400"
         ;;
         g5|970|ppc970|powerpc970)
-            cpuflags="-mcpu=970 -mpowerpc-gfxopt -mpowerpc64"
+            cpuflags="-mcpu=970"
         ;;
         power[3-7]*)
-            cpuflags="-mcpu=$cpu -mpowerpc-gfxopt -mpowerpc64"
+            cpuflags="-mcpu=$cpu"
         ;;
         cell)
             cpuflags="-mcpu=cell"