Update spi_get_erasefn_from_opcode().

We forgot to add a few SPI erase functions to the helper function that is
used for SFDP. Also, sort the declarations in the header.

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

git-svn-id: svn://coreboot.org/flashrom/trunk@1672 2b7e53f0-3cfb-0310-b3e9-8179ed1497e1