drm/i915: Increase gen2 vco frequency limit to 1512 MHz

drm/i915: Increase gen2 vco frequency limit to 1512 MHz

Bruno Prémont has a 855 machine with a 1400x1050 LVDS screen.

The VBT mode is as follows:
0:"1400x1050" 0 108000 1400 1416 1528 1688 1050 1051 1054 1066 0x8 0xa

The BIOS uses the following DPLL settings:
DPLL = 0x90020000
FP0 = 0x2140e
FP1 = 0x21207

That puts the BIOS generated VCO frequency at 1512 MHz, which is
higher than the 1400 MHz limit we have currently.

Let's bump the VCO limit to 1512 MHz and see what happens.

Cc: Bruno Prémont <bonbons@linux-vserver.org>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Tested-by: Bruno Prémont <bonbons@linux-vserver.org>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>