beagle: enable DVI_PUP

beagle: enable DVI_PUP

this patch addresses the issue that there is no DVI output on beagleboard-xm in
u-boot; the TFP410 is not powered on, DVI_PUP needs to be set high

this is done differently on beagleboard-xm rev. B/C versus earlier boards:
beagleboard-xm B/C need to set GPIO2 of the TWL4030
earlier boards need to set GPIO170

note that the change occured somewhere inbetween beagleboard-xm rev. A2 and A3

note that beagleboard-xm rev. A and rev. B cannot be distinguished using
get_board_revision(), REVISION_XM_A/REVISION_XM_B is bogus

due to this glitch, the patch cannot work correctly on some beagleboard-xm
rev A/B boards

tested on beagleboard-xm rev. C (you should see orange color on a monitor)

note that the framebuffer is NOT yet set up, this could be done along the
lines below (for 800x480 resolution and RGB24) before calling omap3_dss_enable()

static void configure_frame_buffer() {
	writel(0x80500000, (uint *) 0x48050480); // address
	writel(0x80500000, (uint *) 0x48050484);
	writel(0x01df031f, (uint *) 0x4805048c); // size
	writel(0x00000091, (uint *) 0x480504a0); // RGB24
}

Signed-off-by: Peter Meerwald <p.meerwald@bct-electronic.com>