serprog: Add support for setting the SPI frequency

Introduce a new opcode (0x14) that sends the requested frequency as a 32b
long value in Hertz to the programmer and receives the frequency eventually
chosen by the programmer. The user can specify this with the programmer
parameter "spispeed" (named after the similar parameter for the buspirate)
including an optional suffix of 'M' or 'k' for specifying megahertz or kilohertz
respectively (lowercase suffixes are also accepted).

Thanks to Idwer and Uwe (and maybe others) for their feedback especially
regarding the unit of frequency to use.

Corresponding to flashrom svn r1571.

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