RISC-V: Comments tidy and improvement.

The GNU coding standards said the comments should be complete sentences
and end with a period and two spaces.  But sometimes it should be more
cleaner when the comments only include a word or codes.  Therefore, I made
the following changes after referring to other target/generic codes,

* Try to write sentences in comments, must end with a period and two spaces.
* End with two spaces without a period for codes/instructions only.
* End with one space without a period for a single word/variable only.

Besids, also rewrite/remove some comments which are obsolete or too long,
and fix indents for comments.

bfd/
    * elfnn-riscv.c: Comments tidy and improvement.
    * elfxx-riscv.c: Likewise.
    * elfxx-riscv.h: Likewise.
gas/
    * config/tc-riscv.c: Comments tidy and improvement.  Also update
    comment "fallthru" to "Fall through" that end with a period and
    two spaces.
include/
    * elf/riscv.h: Comments tidy and improvement.
    * opcode/riscv-opc.h: Likewise.
    * opcode/riscv.h: Likewise.
opcodes/
    * riscv-dis.c: Comments tidy and improvement.
    * riscv-opc.c: Likewise.

1 files changed, 1 insertions, 3 deletions

diff --git a/bfd/elfxx-riscv.h b/bfd/elfxx-riscv.h
index 4d7a6dc..87ebaf4 100644
--- a/bfd/elfxx-riscv.h
+++ b/bfd/elfxx-riscv.h
@@ -90,9 +90,7 @@ riscv_arch_str (unsigned, const riscv_subset_list_t *);
 extern size_t
 riscv_estimate_digit (unsigned);
 
-/* ISA extension name class. E.g. "zbb" corresponds to RV_ISA_CLASS_Z,
-   "xargs" corresponds to RV_ISA_CLASS_X, etc.  */
-
+/* ISA extension prefixed name class.  */
 typedef enum riscv_isa_ext_class
 {
   RV_ISA_CLASS_S,