video: fbdev: pmag-aa-fb: Report video timings

The board uses hardwired timings compatible with 72Hz DEC VR319-DA and
VRM17-AA monitors, according to the board owner's manual[1].  These
timings are accordingly taken from the VR319 manual[2].

References:

[1] "The Monochrome Frame Buffer TURBOchannel Module", Digital Equipment
    Corporation, Order Number: EK-MFBOM-TC-001, December 1991

[2] "Installing and Using the VR319 Monochrome Monitor", Digital
    Equipment Corporation, Order Number: EK-VR319-IN-001, First Edition,
    January 1990, Table 6-1 "Video Timing--1280 x 1024 Resolution"

Signed-off-by: Maciej W. Rozycki <macro@linux-mips.org>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>