ARM: OMAP4: PM: Warn users about usage of older bootloaders

OMAP4 CHIP level PM works only with newer bootloaders. The
dependency on the bootloader comes from the fact that the
kernel is missing reset and initialization code for some
devices.

While the right thing to do is to add reset and init code in
the kernel, for some co-processor IP blocks like DSP and IVA
it means downloading firmware into each one of them to execute
idle instructions.

While a feasible solution is worked upon on how such IP blocks
can be better handled in the kernel, in the interim, to avoid
any further frustration to users testing PM on OMAP4 and finding
it broken, warn them about the bootloader being a possible
cause.

Signed-off-by: Rajendra Nayak <rnayak@ti.com>
Cc: Tero Kristo <t-kristo@ti.com>
Cc: Santosh Shilimkar <santosh.shilimkar@ti.com>
Cc: R Sricharan <r.sricharan@ti.com>
[paul@pwsan.com: tweaked warning messages and comments slightly]
Acked-by: Kevin Hilman <khilman@linaro.org>
[paul@pwsan.com: fixed checkpatch warning]
Signed-off-by: Paul Walmsley <paul@pwsan.com>