mips: syscalls: switch to generic syscalltbl.sh

Many architectures duplicate similar shell scripts.

This commit converts mips to use scripts/syscalltbl.sh. This also
unifies syscall_table_32_o32.h and syscall_table_64_o32.h into
syscall_table_o32.h.

The offset parameters are unneeded here; __SYSCALL(nr, entry) is defined
as 'PTR entry', so the parameter 'nr' is not used in the first place.

With this commit, syscall tables and generated files are straight
mapped,  which makes things easier to understand.

  syscall_n32.tbl  -->  syscall_table_n32.h
  syscall_n64.tbl  -->  syscall_table_n64.h
  syscall_o32.tbl  -->  syscall_table_o32.h

Then, the abi parameters are also unneeded.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>