Refactor Intel Chipset Enables

 - Combine enable_flash_ich_4e() and enable_flash_ich_dc() to
   enable_flash_ich_fwh().
 - Remove unjustified (chipset) name parameters from various
   enable_flash_ich* functions.
 - Make Poulsbo and Tunnel Creek use generic enables by refining existing
   functions to work with them, including everything in ichspi.c.
 - Refactor enable_flash_ich_fwh_decode() to be called unconditionally for
   all chipsets.
 - Add support for Intel Atom Centerton (S12x0).
 - Recombine ICH2/3/4/5 to CHIPSET_ICH2345 because we treat them equally
   anyway.
 - Move spibar handling out of ich_init_spi() into enable_flash_ich_spi()
 - Various small cleanups.

Corresponding to flashrom svn r1761.

Signed-off-by: Stefan Tauner <stefan.tauner@alumni.tuwien.ac.at>
Acked-by: Stefan Tauner <stefan.tauner@alumni.tuwien.ac.at>