Formatting changes for RISC-V

Formatting changes for RISC-V

This is a mixed bag of format changes:

 * Replacing constants with macros (0xffffffff with MINUS_ONE, for
   example).  There's one technically functional change in here (some
   MINUS_ONEs are changed to 0), but it only changes the behavior of an
   otherwise-unused field.
 * Using 0 instead of 0x0 in the relocation table.
 * There were some missing spaces before parens, the spaces have been
   added.
 * A handful of comments are now more descriptive.
 * A bunch of whitespace-only changes, mostly alignment and brace
   newlines.

bfd/
	* elfnn-riscv.c: Formatting and comment fixes throughout.
	* elfxx-riscv.c: Likewise.
	(howto_table): Change the src_mask field from MINUS_ONE to 0 for
	R_RISCV_TLS_DTPMOD32, R_RISCV_TLS_DTPMOD64, R_RISCV_TLS_DTPREL32,
	R_RISCV_TLS_DTPREL64, R_RISCV_TLS_TPREL32, R_RISCV_TLS_TPREL64.
opcodes/
	* riscv-opc.c: Formatting fixes.
gas/
	* config/tc-riscv.c: Formatting and comment fixes throughout.