RISC-V: Support svinval extension with frozen version 1.0.

RISC-V: Support svinval extension with frozen version 1.0.

According to the privileged spec, there are five new instructions for
svinval extension.  Two of them (HINVAL.VVMA and HINVAL.GVMA) need to
enable the hypervisor extension.  But there is no implementation of
hypervisor extension in mainline for now, so let's consider the related
issues later.

                31..25  24..20 19..15 14..12 11...7 6..2  1..0
sinval.vma      0001011 rs2    rs1    000    00000  11100 11
sfence.w.inval  0001100 00000  00000  000    00000  11100 11
sfence.inval.ir 0001100 00001  00000  000    00000  11100 11
hinval.vvma     0010011 rs2    rs1    000    00000  11100 11
hinval.gvma     0110011 rs2    rs1    000    00000  11100 11

This patch is cherry-picked from the riscv integration branch since the
svinval extension is frozen for now.  Besides, we fix the funct7 encodings
of hinval.vvma and hinval.gvma, from 0x0011011 and 0x0111011 to 0x0010011
and 0x0110011.

bfd/
	* elfxx-riscv.c (riscv_supported_std_s_ext): Added svinval.
	(riscv_multi_subset_supports): Handle INSN_CLASS_SVINVAL.
gas/
	* testsuite/gas/riscv/svinval.d: New testcase.
	* testsuite/gas/riscv/svinval.s: Likewise.
include/
	* opcode/riscv-opc.h: Added encodings for svinval.
	* opcode/riscv.h (enum riscv_insn_class): Added INSN_CLASS_SVINVAL.
opcodes/
	* riscv-opc.c (riscv_opcodes): Added svinval instructions.