ARM: OMAP3: Fix idle mode signaling for sys_clkreq and sys_off_mode

While debugging legacy mode vs device tree booted PM regressions,
I noticed that omap3 is not toggling sys_clkreq and sys_off_mode
pins like it should.

The sys_clkreq and sys_off_mode pins are not toggling because of
the following issues:

1. The default polarity for the sys_off_mode pin is wrong.
   OFFMODE_POL needs to be cleared for sys_off_mode to go down when
   hitting off-idle, while CLKREQ_POL needs to be set so sys_clkreq
   goes down when hitting retention.

2. The values for voltctrl register need to be updated dynamically.
   We need to set either the retention idle bits, or off idle bits
   in the voltctrl register depending the idle mode we're targeting
   to hit.

Let's fix these two issues as otherwise the system will just
hang if any twl4030 PMIC idle scripts are loaded. The only case
where the system does not hang is if only retention idle over I2C4
is configured by the bootloader.

Note that even without the twl4030 PMIC scripts, these fixes will
do the proper signaling of sys_clkreq and sys_off_mode pins, so
the fixes are needed to fix monitoring of PM states with LEDs or
an oscilloscope.

Cc: Kevin Hilman <khilman@linaro.org>
Cc: Nishanth Menon <nm@ti.com>
Cc: Paul Walmsley <paul@pwsan.com>
Cc: Tero Kristo <t-kristo@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>