flashrom: Bump to version 0.9.8

This version adds support for new Intel SoC (e.g. BayTrail) and
spi over usb devices such as pickit2 and ftdi usb-spi.

[Thomas:
  - add missing Config.in comment about the thread dependency
  - remove 'Requires PCIUtils libraries' from the Config.in help text,
    since flashrom now requires more than PCIUtils library, and we
    typically don't document such dependencies in Config.in help
    texts.]

Signed-off-by: Florent Valette <florent.valette@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>