doc, riscv: Clean up documentation of RISC-V options [PR122243]

doc, riscv: Clean up documentation of RISC-V options [PR122243]

gcc/ChangeLog
	PR other/122243
	* config/riscv/riscv.opt (mplt): Mark deprecated option Undocumented.
	(msmall-data-limit=): Mark RejectNegative.
	* doc/invoke.texi (Option Summary) <RISC-V Options>:  Remove -mplt
	documentation.  Only list one form of each option.  Add missing
	options -mcpu, -mscalar-strict-align, -mno-vector-strict-align,
	-momit-leaf-frame-pointer, -mstringop-strategy, -mrvv-vector-bits,
	-mrvv-max-lmul, -madjust-lmul-cost, -mmax-vectorization, and
	-mno-autovec-segment.
	(RISC-V Options):  Remove -mplt documentation.  Add documentation for
	missing options listed above.  Add missing index entries for negative
	forms.  Correct the default for the -minline-str* options, which
	has changed.  Copy-edit for markup, spelling, and usage.  Trivial
	whitespace fixes.