[PATCH] I2C: i2c-piix4: Remove the fix_hstcfg parameter

This patch removes the fix_hstcfg option from the driver and related
SMBus Interrupt Select register magic because now we know what are
valid values for this register. This patch updates the documentation
and adds new IRQ mode check so we are sure not to miss any new
"unusual" value.

The PCI quirk for users of fix_hstcfg was not developed because the
chipset lacks of subsystem ID registers and DMI is stated "To be
filled". Impact to existing systems is minimal because the problem
showed up on motherboards like 10 years back. On the other hand users
of newer Serverworks and HT1000 systems won't be misleaded by the
message suggesting to try the fix_hstcfg any more.

Signed-off-by: Rudolf Marek <r.marek@sh.cvut.cz>
Signed-off-by: Jean Delvare <khali@linux-fr.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>