riscv: Fix CONFIG_AS_HAS_INSN for new .insn usage

riscv: Fix CONFIG_AS_HAS_INSN for new .insn usage

After commit 44aa25c000b4 ("riscv: asm: use .insn for making custom
instructions"), builds using LLVM older that 19 or binutils older than
2.38 fail with:

  arch/riscv/include/asm/vdso/processor.h: Assembler messages:
  arch/riscv/include/asm/vdso/processor.h:27: Error: unrecognized opcode `0x100000f'
  arch/riscv/include/asm/vdso/processor.h:27: Error: unrecognized opcode `0x100000f'
  arch/riscv/include/asm/vdso/processor.h:27: Error: unrecognized opcode `0x100000f'
  arch/riscv/include/asm/vdso/processor.h:27: Error: unrecognized opcode `0x100000f'
  make[4]: *** [scripts/Makefile.build:287: arch/riscv/kernel/vdso/vgettimeofday.o] Error 1

  In file included from <built-in>:4:
  In file included from lib/vdso/gettimeofday.c:6:
  In file included from include/vdso/datapage.h:21:
  In file included from include/vdso/processor.h:10:
  arch/riscv/include/asm/vdso/processor.h:23:2: error: expected instruction format
     23 |         ALT_RISCV_PAUSE();
        |         ^
  arch/riscv/include/asm/errata_list.h:47:3: note: expanded from macro 'ALT_RISCV_PAUSE'
     47 |                 RISCV_PAUSE, /* Original RISC‑V pause insn */ \
        |                 ^
  arch/riscv/include/asm/insn-def.h:259:21: note: expanded from macro 'RISCV_PAUSE'
    259 | #define RISCV_PAUSE     ASM_INSN_I("0x100000f")
        |                         ^
  arch/riscv/include/asm/asm.h:16:26: note: expanded from macro 'ASM_INSN_I'
     16 | #define ASM_INSN_I(__x) ".insn " __x
        |                          ^
  <inline asm>:5:7: note: instantiated into assembly here
      5 | .insn 0x100000f
        |       ^

binutils gained support for '.insn <value>' in 2.38 [1] and LLVM gained
support in 19 [2]. Adjust the test for CONFIG_AS_HAS_INSN to ensure that
all versions of .insn are supported before being used.

Fixes: 44aa25c000b4 ("riscv: asm: use .insn for making custom instructions")
Link: https://sourceware.org/git/?p=binutils-gdb.git;a=commit;h=a262b82fdbf4cda3b0648b1adc32245ca3f78b7a
Link: https://github.com/llvm/llvm-project/commit/2a086dce691e3cc34a2fc27f4fb255bb2cbbfac9
Suggested-by: Andrew Jones <ajones@ventanamicro.com>
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
Link: https://patch.msgid.link/20251107-riscv-fix-new-insn-usage-v1-1-9a186c5928a0@kernel.org
Signed-off-by: Paul Walmsley <pjw@kernel.org>