OMAP2 clock: split OMAP2420, OMAP2430 clock data into their own files

In preparation for multi-OMAP2 kernels, split
mach-omap2/clock2xxx_data.c into mach-omap2/clock2420_data.c and
mach-omap2/clock2430_data.c.  2430 uses a different device space
physical memory layout than past or future OMAPs, and we use a
different virtual memory layout as well, which causes trouble for
architecture-level code/data that tries to support both.  We tried
using offsets from the virtual base last year, but those patches never
made it upstream; so after some discussion with Tony about the best
all-around approach, we'll just grit our teeth and duplicate the
structures.  The maintenance advantages of a single kernel config that
can compile and boot on OMAP2, 3, and 4 platforms are simply too
compelling.

This approach does have some nice benefits beyond multi-OMAP 2 kernel
support.  The runtime size of OMAP2420-specific and OMAP2430-specific
kernels is smaller, since unused clocks for the other OMAP2 chip will
no longer be compiled in.  (At some point we will mark the clock data
__initdata and allocate it during registration, which will eliminate
the runtime memory advantage.)  It also makes the clock trees slightly
easier to read, since 2420-specific and 2430-specific clocks are no
longer mixed together.

This patch also splits 2430-specific clock code into its own file,
mach-omap2/clock2430.c, which is only compiled in for 2430 builds -
mostly for organizational clarity.

While here, fix a bug in the OMAP2430 clock tree: "emul_ck" was
incorrectly marked as being 2420-only, when actually it is present on
both OMAP2420 and OMAP2430.

Thanks to Tony for some good discussions about how to approach this
problem.

Signed-off-by: Paul Walmsley <paul@pwsan.com>
Cc: Tony Lindgren <tony@atomide.com>
Cc: Richard Woodruff <r-woodruff2@ti.com>