RISC-V: Remove the unimplemented extensions.

Although spec had defined and ratified p, v and n extensions,
but we don't have any related implementaitons so far, so keep
them in the supported extension table looks weird.  Remove them
until we have the related implementations.

	opcodes/
	* riscv-opc.c (riscv_ext_version_table): Remove the p, v, n
	and their versions.

opcodes/ChangeLog

@@ -1,3 +1,8 @@
+2020-12-01  Nelson Chu  <nelson.chu@sifive.com>
+
+	* riscv-opc.c (riscv_ext_version_table): Remove the p, v, n
+	and their versions.
+
 2020-12-01  Nelson Chu  <nelson.chu@sifive.com>
 
 	* riscv-opc.c (riscv_ext_version_table): Add zifencei.

opcodes/riscv-opc.c

@@ -921,17 +921,6 @@ const struct riscv_ext_version riscv_ext_version_table[] =
 {"c", ISA_SPEC_CLASS_20190608, 2, 0},
 {"c", ISA_SPEC_CLASS_2P2,      2, 0},
 
-{"p", ISA_SPEC_CLASS_20191213, 0, 2},
-{"p", ISA_SPEC_CLASS_20190608, 0, 2},
-{"p", ISA_SPEC_CLASS_2P2,      0, 1},
-
-{"v", ISA_SPEC_CLASS_20191213, 0, 7},
-{"v", ISA_SPEC_CLASS_20190608, 0, 7},
-{"v", ISA_SPEC_CLASS_2P2,      0, 7},
-
-{"n", ISA_SPEC_CLASS_20190608, 1, 1},
-{"n", ISA_SPEC_CLASS_2P2,      1, 1},
-
 {"zicsr", ISA_SPEC_CLASS_20191213, 2, 0},
 {"zicsr", ISA_SPEC_CLASS_20190608, 2, 0},