Add additional SPI sector erase and chip erase command functions to

Add additional SPI sector erase and chip erase command functions to
flashrom. Not all chips support all commands, so allow the implementer
to select the matching function.
Fix a layering violation in ICH SPI code to be less bad. Still not
perfect, but the new code is shorter, more generic and
architecturally
more sound.

TODO (in a separate patch):
- move the generic sector erase code to spi.c
- decide which erase command to use based on info about the chip
- create a generic spi_erase_all_sectors function which calls the
generic sector erase function

Thanks to Stefan for reviewing and commenting.

Signed-off-by: Carl-Daniel Hailfinger <c-d.hailfinger.devel.2006@gmx.net>
Acked-by: Stefan Reinauer <stepan@coresystems.de>
git-svn-id: svn://svn.coreboot.org/coreboot/trunk@3722 2b7e53f0-3cfb-0310-b3e9-8179ed1497e1