mpc5200, digsy_mtc: add support for rev5 board version

difference to previous board version:
- M29W128GH flash from Numonyx
- SDRAM ISSI IS45S16800 (Option A2 105°C)
- rev5 uses RTC RV-3029-C2
- update cs0 and cs1 baseaddr and length
  depending on the detected flash size.
- added Werner Pfister <Pfister_Werner@intercontrol.de>
  as maintainer for the digsy board variants
- As the M29W128GH needs a special flash_cmd_reset()
  document that in the new file doc/README.cfi.
- move "#endif /* CONFIG_CMD_IDE */" to the right place
- remove LOWBOOT config option for digsy_mtc and digsy_mtc_rev5
  boards
- change doc/README.cfi as Stefan Roese suggested

Signed-off-by: Heiko Schocher <hs@denx.de>
Signed-off-by: Stefan Roese <sr@denx.de>
Acked-by: Detlev Zundel <dzu@denx.de>
cc: Wolfgang Denk <hs@denx.de>
cc: Stefan Roese <sr@denx.de>
cc: Werner Pfister <Pfister_Werner@intercontrol.de>
cc: Detlev Zundel <dzu@denx.de>