ramips: improve sysupgrade helpers for I-O DATA devices

ramips: improve sysupgrade helpers for I-O DATA devices

I-O DATA devices manufactured by MSTC (MitraStar Technology Corp.)
have some important flags for booting, "bootnum" and "debugflag".
The almost devices have both flags but some devices have only
"bootnum" flag.
So optimize helper functions in iodata.sh to set each flags.

- both:
  - WN-AX1167GR2
  - WN-AX2033GR
  - WN-DX1167R
  - WN-DX1200GR
  - WN-DX2033GR

- "bootnum" only
  - WN-DEAX1800GR

Signed-off-by: INAGAKI Hiroshi <musashino.open@gmail.com>