aarch64: Fix bf16_v(ld|st)n.c failures for big-endian

gcc.target/aarch64/advsimd-intrinsics/bf16_vldn.c and
gcc.target/aarch64/advsimd-intrinsics/bf16_vstn.c were
failing for big-endian targets because the <Vmtype> in
aarch64_be_ld1<mode> and aarch64_be_st1<mode> had no
expansion for the bfloat16 modes.

2020-03-17  Richard Sandiford  <richard.sandiford@arm.com>

gcc/
	* config/aarch64/iterators.md (Vmtype): Handle V4BF and V8BF.

gcc/ChangeLog

+2020-03-17  Richard Sandiford  <richard.sandiford@arm.com>
+
+	* config/aarch64/iterators.md (Vmtype): Handle V4BF and V8BF.
+
 2020-03-17  Andre Vieira  <andre.simoesdiasvieira@arm.com>
             Mihail Ionescu  <mihail.ionescu@arm.com>
             Srinath Parvathaneni  <srinath.parvathaneni@arm.com>

gcc/config/aarch64/iterators.md

@@ -1000,7 +1000,8 @@
 			 (V4HI ".4h") (V8HI  ".8h")
 			 (V2SI ".2s") (V4SI  ".4s")
 			 (V2DI ".2d") (V4HF ".4h")
-			 (V8HF ".8h") (V2SF ".2s")
+			 (V8HF ".8h") (V4BF ".4h")
+			 (V8BF ".8h") (V2SF ".2s")
 			 (V4SF ".4s") (V2DF ".2d")
 			 (DI   "")    (SI   "")
 			 (HI   "")    (QI   "")