Fill in the function that finds the GPIO base

Finds the GPIO base value to use in the GPIO number calculation.

This is most likely specific to ASPEED BMCs, though as with
the calling code additional support can be added in the
future if required.

Change-Id: Ie0d2b87286ab4bf6b05b61245bd821ab2a9d602a
Signed-off-by: Matt Spinler <spinler@us.ibm.com>
1 file changed