RISC-V: Update syscall list for 32-bit support.

RISC-V: Update syscall list for 32-bit support.

32-bit RISC-V uses _llseek instead of lseek as syscall number 62.
Update syscall list from open-embedded build, primarily because
32-bit RISC-V requires statx support.

Tested with cross gcc testsuite runs for rv32 and rv64, with the
pending statx patch also applied.

Signed-off-by: Jim Wilson <jimw@sifive.com>
Reviewed-by: Laurent Vivier <laurent@vivier.eu>
Signed-off-by: Palmer Dabbelt <palmer@sifive.com>