linux-user, mips: add syscall table generation support

Copy syscall.tbl and syscallhdr.sh from linux/arch/mips/kernel/syscalls/syscall_o32.tbl v5.5
Update syscallhdr.sh to generate QEMU syscall_nr.h
Move the offset (4000) from the file to the Makefile.objs to be passed
to syscallhdr.sh
Rename on the fly fadvise64 to fadvise64_64.

Signed-off-by: Laurent Vivier <laurent@vivier.eu>
Reviewed-by: Taylor Simpson <tsimpson@quicinc.com>
Message-Id: <20200310103403.3284090-17-laurent@vivier.eu>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>
6 files changed