x86: gpio: Add additional GPIO banks to the ICH6 driver

We can generally trust the ICH to have GPIO Bank 0 (the first 32 pins) in the
same place across all versions. This change adds two more banks, for up to
96 GPIOS.

BUT:
- Not all chipsets have the same number of GPIOs
- Not all chipsets have the same number of GPIO banks
- Not all chipsets put the additional banks at the same offset from GPIOBASE
- There so many chipset variants that it's pretty much impossible to support
  them all, or even keep track of the new ones.

So, although this adds suppport for the additional banks that seem to work
for the particular variants of CougarPoint Mobile chipsets that we've tried,
there's no chance it will support everything Intel produces. Good luck.

Signed-off-by: Bill Richardson <wfrichar@chromium.org>
Signed-off-by: Simon Glass <sjg@chromium.org>