Microchip MEC172X: Rework GPIO definitions to separate package types.

MEC172X has 2 package sizes with additional pins on the -LJ package.
This commit separates the package-specific parts into different files.
In addition, this patch removes unnecessary package-specific enums in
favor of calculated offsets into the desired registers.

Signed-off-by: Jeff Daly <jeffd@silicom-usa.com>