RISC-V: Minimal support of scalar crypto extension.

Minimal support of scalar crypto extension, add "k" in the
riscv_supported_std_ext, to make the order check right with
"zk" behind "zb".

bfd/
	* elfxx-riscv.c (riscv_implicit_subsets): Added implicit
	rules for zk* extensions.
	(riscv_supported_std_ext): Added entry for k.
	(riscv_supported_std_z_ext): Added entries for zk*.
diff --git a/bfd/elfxx-riscv.c b/bfd/elfxx-riscv.c
index 3ffbaad..9879480 100644
--- a/bfd/elfxx-riscv.c
+++ b/bfd/elfxx-riscv.c
@@ -1075,6 +1075,20 @@
   {"q", "d",		check_implicit_always},
   {"d", "f",		check_implicit_always},
   {"f", "zicsr",	check_implicit_always},
+  {"zk", "zkn",		check_implicit_always},
+  {"zk", "zkr",		check_implicit_always},
+  {"zk", "zkt",		check_implicit_always},
+  {"zkn", "zbkb",	check_implicit_always},
+  {"zkn", "zbkc",	check_implicit_always},
+  {"zkn", "zbkx",	check_implicit_always},
+  {"zkn", "zkne",	check_implicit_always},
+  {"zkn", "zknd",	check_implicit_always},
+  {"zkn", "zknh",	check_implicit_always},
+  {"zks", "zbkb",	check_implicit_always},
+  {"zks", "zbkc",	check_implicit_always},
+  {"zks", "zbkx",	check_implicit_always},
+  {"zks", "zksed",	check_implicit_always},
+  {"zks", "zksh",	check_implicit_always},
   {NULL, NULL, NULL}
 };
 
@@ -1127,6 +1141,7 @@
   {"c",		ISA_SPEC_CLASS_20190608,	2, 0, 0 },
   {"c",		ISA_SPEC_CLASS_2P2,		2, 0, 0 },
   {"b",		ISA_SPEC_CLASS_NONE, RISCV_UNKNOWN_VERSION, RISCV_UNKNOWN_VERSION, 0 },
+  {"k",		ISA_SPEC_CLASS_NONE, RISCV_UNKNOWN_VERSION, RISCV_UNKNOWN_VERSION, 0 },
   {"j",		ISA_SPEC_CLASS_NONE, RISCV_UNKNOWN_VERSION, RISCV_UNKNOWN_VERSION, 0 },
   {"t",		ISA_SPEC_CLASS_NONE, RISCV_UNKNOWN_VERSION, RISCV_UNKNOWN_VERSION, 0 },
   {"p",		ISA_SPEC_CLASS_NONE, RISCV_UNKNOWN_VERSION, RISCV_UNKNOWN_VERSION, 0 },
@@ -1145,7 +1160,20 @@
   {"zbb",		ISA_SPEC_CLASS_DRAFT,		1, 0,  0 },
   {"zba",		ISA_SPEC_CLASS_DRAFT,		1, 0,  0 },
   {"zbc",		ISA_SPEC_CLASS_DRAFT,		1, 0,  0 },
-  {"zbs",               ISA_SPEC_CLASS_DRAFT,           1, 0,  0 },
+  {"zbs",		ISA_SPEC_CLASS_DRAFT,		1, 0,  0 },
+  {"zbkb",		ISA_SPEC_CLASS_DRAFT,		1, 0,  0 },
+  {"zbkc",		ISA_SPEC_CLASS_DRAFT,		1, 0,  0 },
+  {"zbkx",		ISA_SPEC_CLASS_DRAFT,		1, 0,  0 },
+  {"zk",		ISA_SPEC_CLASS_DRAFT,		1, 0,  0 },
+  {"zkn",		ISA_SPEC_CLASS_DRAFT,		1, 0,  0 },
+  {"zknd",		ISA_SPEC_CLASS_DRAFT,		1, 0,  0 },
+  {"zkne",		ISA_SPEC_CLASS_DRAFT,		1, 0,  0 },
+  {"zknh",		ISA_SPEC_CLASS_DRAFT,		1, 0,  0 },
+  {"zkr",		ISA_SPEC_CLASS_DRAFT,		1, 0,  0 },
+  {"zks",		ISA_SPEC_CLASS_DRAFT,		1, 0,  0 },
+  {"zksed",		ISA_SPEC_CLASS_DRAFT,		1, 0,  0 },
+  {"zksh",		ISA_SPEC_CLASS_DRAFT,		1, 0,  0 },
+  {"zkt",		ISA_SPEC_CLASS_DRAFT,		1, 0,  0 },
   {NULL, 0, 0, 0, 0}
 };