ARM: OMAP2+: powerdomain code: Fix Wake-up power domain power status

ARM: OMAP2+: powerdomain code: Fix Wake-up power domain power status

The wake-up power domain is an alway-on power domain and so this power domain
does not have a power state status (PM_PWSTST_xxx) register that indicates the
current state. However, during the registering of the wake-up power domain the
state of the domain is queried by calling pwrdm_read_pwrst(). This actually
tries to read a register that does not exist and returns a value of 0 that
indicates that the current state is OFF. The OFF state count of the wake-up
power domain is then set to 1 and the current state to OFF. Both of which are
incorrect.

To fix this, if a power domain only supports the ON state, do not attempt to
read the power state status register and simply return ON as the current power
state.

This is based upon Tony's current linux-omap master branch.

Testing:
- Boot tested on OMAP4460 panda.
- Boot tested on OMAP3430 beagle and validated CORE RET still working (using
  Paul's 32k timer patch [1]).

[1] http://marc.info/?l=linux-omap&m=134000053229888&w=2

Signed-off-by: Jon Hunter <jon-hunter@ti.com>
Acked-by: Kevin Hilman <khilman@ti.com>
Acked-by: Santosh Shilimkar <santosh.shilimkar@ti.com>
[paul@pwsan.com: edited commit message slightly]
Signed-off-by: Paul Walmsley <paul@pwsan.com>