savagefb: Use panel CVT mode as default

If there is no EDID but an LCD panel is detected, generate a CVT
mode from the panel resolution (at 60 Hz), and use this as a
default mode instead of the hardcoded 800x600x8 mode.

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