ARM: OMAP2+: board-generic: update SoC compatibility strings

Now that we have standardized SoC definitions, update the
compatibility strings in board machine descriptors. Eventually, we
should just have SoC compatiblity here and all board specific stuff
should disappear.

Signed-off-by: Nishanth Menon <nm@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>