Introduce OS specific cmdline argument handling and move SMB arg to os-posix.c

Introduce OS specific cmdline argument handling by calling
os_parse_cmd_args() at the end of switch() statement. Move option
enum to qemu-options.h and have it included from os-posix.c and
os-win32.c in addition to vl.c.

In addition move SMB argument to os-posix.c

Signed-off-by: Jes Sorensen <Jes.Sorensen@redhat.com>
Acked-by: Juan Quintela <quintela@redhat.com>
Acked-by: Richard Henderson <rth@redhat.com>
Signed-off-by: Blue Swirl <blauwirbel@gmail.com>