intpm(4): Decrease requested i/o port range width

On some AMD FCH devices driven by intpm(4) (read: mine), the SMBus I/O port
range is split in two and the low range is only 0x10 wide. intpm(4) does
not access any registers above 0x0f, so there is no need for the wider
range.

Discussed with: avg
Sponsored by: Dell EMC Isilon