savagefb: Set up I2C based on chip family instead of card id

In practice this means enabling I2C (for DDC2) on all prosavage cards,
like the xorg ddx does. The savage4 and savage2000 families have only
one member each, so there is no change for those.

Tested on TwisterK.

Signed-off-by: Tormod Volden <debian.tormod@gmail.com>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>