Boxer panel: set timings for 1024x600@90Hz

90 Hz is a reasonable multiple of both 30 Hz and 60 Hz, which should
allow for more visual smoothness with less tearing.

Change-Id: If680ac798ad0db970116331511bacd045b653253
encore local defconfigs: reduce CONFIG_OMAP2_DSS_MIN_FCK_PER_PCK

The maximum FCLK for the DSS is 173 MHz on OMAP3, so given our pixel
clock, the highest value we can set the multiplier to is 2.

Change-Id: I190e24548dd6b4884f37a55500bcfff28bde2839