nvidiafb: Add boot option to reverse i2c port assignment

There are a few nvidia hardware where the i2c port assignments are reversed,
i.e., the 1st i2c port is assigned to the secondary display and the 2nd i2c
port to the primary display.  In most cases, if only 1 display is attached, or
if only 1 flatpanel and 1 analog display is attached, the port reversal is of
no consequence.  However if 2 flatpanels are attached, it can cause display
problems.

There is no sane way of determining if the hardware reversed the i2c port
assignment, so the simplest fix is to add a boot/module option, "reverse_i2c
to explicitly reverse the i2c port.

This also restores i2c ordering back to the pre-2.6.22 state.

Signed-off-by: Antonino Daplas <adaplas@gail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>