[PowerPC][Altivec] Add mfvrd and mffprd extended mnemonic

mfvrd and mffprd are both alias to mfvrsd.
This patch enables correct parsing of the aliases, but we still emit a mfvrsd.

Committing on behalf of brunoalr (Bruno Rosa).

Differential Revision: https://reviews.llvm.org/D29177

llvm-svn: 297849
diff --git a/llvm/test/CodeGen/PowerPC/bitcasts-direct-move.ll b/llvm/test/CodeGen/PowerPC/bitcasts-direct-move.ll
index 79da5cb..d6c7dd3 100644
--- a/llvm/test/CodeGen/PowerPC/bitcasts-direct-move.ll
+++ b/llvm/test/CodeGen/PowerPC/bitcasts-direct-move.ll
@@ -20,7 +20,7 @@
   ret i64 %0
 ; CHECK-P7: stxsdx 1,
 ; CHECK-P7: ld 3,
-; CHECK: mfvsrd 3, 1
+; CHECK: mffprd 3, 1
 }
 
 define float @i32tof32(i32 signext %a) {
@@ -60,7 +60,7 @@
   ret i64 %0
 ; CHECK-P7: stxsdx 1,
 ; CHECK-P7: ld 3,
-; CHECK: mfvsrd 3, 1
+; CHECK: mffprd 3, 1
 }
 
 define float @i32utof32(i32 zeroext %a) {