ARM: OMAP: Split plat/cpu.h into local soc.h for mach-omap1 and mach-omap2

We want to remove plat/cpu.h. To do this, let's first split
it to private soc.h to mach-omap1 and mach-omap2. We have to
keep plat/cpu.h around until the remaining drivers are fixed,
so let's include the local soc.h in plat/cpu.h and for drivers
still including plat/cpu.h.

Once the drivers are fixed not to include plat/cpu.h, we
can remove the file.

This is needed for the ARM common zImage support.

[tony@atomide.com: updated to not print a warning]
Signed-off-by: Tony Lindgren <tony@atomide.com>