2.4.19 IDE SIS, 133 and latest 100 chipsets UDMA support

Hello,

here's a patch against 2.4.19 / 2.4.20-pre1 that brings support for UltraDMA on newest SiS chipsets. This brings the main tree SiS IDE support to AC tree level.

As always, any failure/success report is welcomed.

Note: I'm already aware of a minor bug with 630ET and 630ST chipsets that clamps udma modes to UDMA4 instead of UDMA5.

LB