Remove mknod wrapper functions, move them to symbols

Remove mknod wrapper functions, move them to symbols

This patch removes the mknod and mknodat static wrapper and add the
symbols on the libc with the expected names.

Both the prototypes of the internal symbol linked by the static
wrappers and the inline redirectors are also removed from the installed
sys/stat.h header file.  The wrapper implementation license LGPL
exception is also removed since it is no longer statically linked to
binaries.

Internally the _STAT_VER* definitions are moved to the arch-specific
xstatver.h file.

Checked with a build for all affected ABIs. I also checked on x86_64,
i686, powerpc, powerpc64le, sparcv9, sparc64, s390, and s390x.

Reviewed-by: Lukasz Majewski <lukma@denx.de>