ARM: OMAP4470: Fix OMAP4470 boot failure

OMAP4470 currently fails to boot, printing various messages such as ...

omap_hwmod: mpu: cannot clk_get main_clk dpll_mpu_m2_ck
omap_hwmod: mpu: cannot _init_clocks
------------[ cut here ]------------
WARNING: at arch/arm/mach-omap2/omap_hwmod.c:2062 _init+0x2a0/0x2e4()
omap_hwmod: mpu: couldn't init clocks
Modules linked in:
[<c001c7fc>] (unwind_backtrace+0x0/0xf4) from [<c0043c64>] (warn_slowpath_common+0x4c/0x64)
[<c0043c64>] (warn_slowpath_common+0x4c/0x64) from [<c0043d10>] (warn_slowpath_fmt+0x30/0x40)
[<c0043d10>] (warn_slowpath_fmt+0x30/0x40) from [<c0674208>] (_init+0x2a0/0x2e4)
[<c0674208>] (_init+0x2a0/0x2e4) from [<c067428c>] (omap_hwmod_setup_one+0x40/0x60)
[<c067428c>] (omap_hwmod_setup_one+0x40/0x60) from [<c0674280>] (omap_hwmod_setup_one+0x34/0x60)
[<c0674280>] (omap_hwmod_setup_one+0x34/0x60) from [<c06726f4>] (omap_dm_timer_init_one+0x30/0x250)
[<c06726f4>] (omap_dm_timer_init_one+0x30/0x250) from [<c0672930>] (omap2_gp_clockevent_init+0x1c/0x108)
[<c0672930>] (omap2_gp_clockevent_init+0x1c/0x108) from [<c0672c60>] (omap4_timer_init+0x10/0x5c)
[<c0672c60>] (omap4_timer_init+0x10/0x5c) from [<c066c418>] (time_init+0x20/0x30)
[<c066c418>] (time_init+0x20/0x30) from [<c0668814>] (start_kernel+0x1b0/0x304)
[<c0668814>] (start_kernel+0x1b0/0x304) from [<80008044>] (0x80008044)
---[ end trace 1b75b31a2719ed1c ]---

The problem is that currently none of the clocks are being registered for
OMAP4470 devices and so on boot-up no clocks can be found and the kernel panics.

This fix allows the kernel to boot without failure using a simple RAMDISK file
system on OMAP4470 blaze board.

Per feedback from Paul and Benoit the 4470 clock data is incomplete for new
modules such as the 2D graphics block that has been added to the 4470.
Therefore add a warning to indicate that the clock data is incomplete.

Cc: Paul Walmsley <paul@pwsan.com>
Cc: Benoit Cousson <b-cousson@ti.com>
Signed-off-by: Jon Hunter <jon-hunter@ti.com>
[tony@atomide.com: updated comments]
Signed-off-by: Tony Lindgren <tony@atomide.com>