arm: Remove OMAP2420H4 and all omap24xx support

The omap2420H4 was the only mainline omap24xx board.  Prior to being
fixed by Jon Hunter in time for v2013.04 it had been functionally broken
for a very long time.  Remove this board as there's not been interest in
it in U-Boot for quite a long time.

Signed-off-by: Tom Rini <trini@ti.com>

Conflicts:
	board/icpdas/lp8x4x/Makefile