RISC-V: Clean up redundant code and fix GNU coding style issues

Tidy up a few non-functional issues in the RISC-V backend.
genrvv-type-indexer.cc includes <assert.h> but uses no assert, and
riscv-v.cc includes "targhooks.h" twice; remove both.  In addition,
riscv_output_move and riscv_save_libcall_count call abort () where
gcc_unreachable () is the preferred idiom for unreachable points.

The remaining changes fix GNU coding style: add the missing space before
the open parenthesis of function calls and casts, fix brace placement,
remove a stray double semicolon and re-wrap a few over-long lines.

All of the above is redundant code, an idiom change or formatting, so
this is a cleanup with no functional change.  No test case is added as
no behaviour changes.

gcc/ChangeLog:

	* common/config/riscv/riscv-common.cc: Fix formatting.
	* config/riscv/gen-riscv-mcpu-texi.cc: Likewise.
	* config/riscv/gen-riscv-mtune-texi.cc: Likewise.
	* config/riscv/genrvv-type-indexer.cc: Remove unused <assert.h>
	include.
	* config/riscv/riscv-string.cc: Fix formatting.
	* config/riscv/riscv-target-attr.cc: Likewise.
	* config/riscv/riscv-v.cc: Remove duplicate "targhooks.h" include.
	Fix formatting.
	* config/riscv/riscv-v.h: Fix formatting.
	* config/riscv/riscv-vsetvl.cc: Likewise.
	* config/riscv/riscv.cc (riscv_pass_by_reference): Remove stray
	double semicolon.  Fix formatting elsewhere.
	(riscv_output_move): Use gcc_unreachable () instead of abort ().
	(riscv_save_libcall_count): Use gcc_unreachable () instead of
	abort ().
	* config/riscv/riscv.h: Fix formatting.
	* config/riscv/thead.cc: Likewise.