tools/include: Sync asm-generic/bitops/fls.h with the kernel sources

To pick up the changes from:

  cb4ede92 ("riscv: Avoid code duplication with generic bitops implementation")

This should address these tools/perf build warnings:

  Warning: Kernel ABI header differences:
    diff -u tools/include/asm-generic/bitops/__fls.h include/asm-generic/bitops/__fls.h
    diff -u tools/include/asm-generic/bitops/fls.h include/asm-generic/bitops/fls.h

Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Palmer Dabbelt <palmer@rivosinc.com>
Cc: linux-arch@vger.kernel.org
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Link: https://lore.kernel.org/r/20240408185520.1550865-9-namhyung@kernel.org